Single crystal growing method

ABSTRACT

A process is disclosed for continuously producing a single crystal by drawing downwardly a melt of a single crystal raw material, wherein a single crystal body grown from the melt is continuously pulled downwardly, and a plurality of single crystal products are continuously formed by intermittently cutting the single crystal body being downwardly moved.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a process and an apparatus forproducing single crystals.

2. Related Art Statement

In order to grow oxide-series single crystals, a process for producingsingle crystal fibers by an μ pulling down process has recentlyattracted attention. "Electrotechnical Laboratory" No. 522, pp 4-8, Jul.1993 describes the story that a single crystal fiber made of potassiumlithium niobate (K₃ Li_(2-2x) Nb_(5+x) O_(15+x), hereinafter referred toas "KLN") was grown by this process.

According to this literature, electric power is fed to a cell orcrucible made of platinum to resistively heat a raw material powder. Amelt drawing hole is formed in the bottom of the cell or crucible, a rodmember called a melt feeder is inserted into this drawing hole so thatboth a feed amount of the melt to the melt drawing hole and the state ofan interface between a liquid phase and a solid phase may be controlled.A thin KLN single crystal fiber is continuously formed, while thediameter of the melt drawing hole, the diameter of the feeder, theprotruded length of the feeder from the drawing hole, etc. arecontrolled. According to this μ pulling down process, the single crystalfiber having the diameter not greater than 1 mm can be formed, and it iseasily possible to reduce thermal strain and to control the convectionof the melt and the diameter of the single crystal fiber. This processalso enables the production of a small size high quality single crystalsuitable particularly for the blue laser device by second harmonicgeneration (SHG).

SUMMARY OF THE INVENTION

The present inventors have repeatedly studied to mass-produce KLN singlecrystal fibers, etc. by using the above μ pulling down process. What isthe most important for the mass production technique are that a largeamount of a melt is treated with an enlarged scale of the crucible, andthat a long single crystal fiber is continuously pulled down from thiscrucible. However, a concrete technique has not yet been known, whichenables the single crystal fiber to be continuously pulled down with useof such a large amount of the raw material.

In view of this, the present inventors carried out the μ pulling downprocess by using an increased amount up to about 5 g of the raw materialpowder to be fed into the crucible, correspondingly enlarging the sizeof the crucible, and melting the raw material powder under heatingthrough feeding electric power to the crucible.

However, when the scale of the crucible was increased and the amount ofthe melted powder was increased, it was found extremely difficult toform the single crystal by drawing the melt through the drawing hole.More specifically, when the temperature inside a furnace in which thecrucible was placed was set as low as not more than 900° C. and thepowder was melted inside the crucible by passing electric current mainlythrough the crucible, the single crystal was not excellently grown inthe vicinity of the drawing hole. That is, when the electric power to befed to the crucible was increased, the melt was kept melted and notcrystallized at the drawing hole. On the other hand, when the electricpower was decreased, the melt was so solidified in the vicinity of thedrawing hole that the melt could not be drawn.

When the above furnace temperature was set beyond 900° C., the entirecrucible was largely heated by radiant heat from the furnace, so thatthe temperature gradient become extremely small in the vicinity of thedrawing hole. In this case, the crystallization growth could not becontinuously effected, either.

In order to solve the above problem, the present inventors havedeveloped a process for continuously drawing a single crystal fiber.This process will be explained later. However, it was found that eventhis process still had a problem particularly from the standpoint ofmass-producing the single crystal fiber by continuously pulling down.

That is, it is necessary to prevent changes in the quality,particularly, in the composition of the single crystal fiber.Particularly, when a material for second harmonic generation or solidlaser elements is to be produced, slight change in the compositionlargely changes its characteristics to make the resulting productunacceptable. Therefore, it is necessary to prevent changes in thecomposition in continuously pulling down the single crystal fiber.

In the conventional μ pulling down process, the composition of thesingle crystal fiber has been examined after growth. Indeed, thecomposition of the produced single crystal fiber can be detected bycutting off a portion of the single crystal fiber and examining itscomposition. But, since the single crystal fiber-growing process basedon the μ pulling down process is a complicated, delicate, chemical andrheological system in which a number of various factors are correlatedwith one another, the composition of the single crystal fiber will oftenchange in such a production system due to slight changes in theproducing condition. As a result, since all of the numerous singlecrystal fibers may be unacceptable, any countermeasure is indispensablefrom the standpoint of the production yield.

It is an object of the present invention to provide a concrete mechanismfor mass-producing an oxide-series single crystal by continuouslypulling down based on the μ pulling down process.

It is another object of the present invention to enable the productionof an oxide-series single crystal having a good quality by continuouslypulling down based on the μ pulling down process, even if the size ofthe crucible is increased or the amount of the raw material isincreased.

It is a further object of the present invention to enable themass-production of an oxide-series single crystal by pulling down basedon the μ pulling down process through continuously treating a largeamount of the raw material.

It is a still further object of the present invention to enable theproduction of an oxide-series single crystal by continuously pullingdown based on the μ pulling down process, while by real-time detectingchanges in the composition of the oxide-series single crystal, changesin the composition of the oxide-series single crystal are prevented andthe yield thereof is largely increased.

A first aspect of the present invention relates to a process forcontinuously producing a single crystal by drawing down a melt of asingle crystal raw material, wherein a single crystal body grown fromthe melt is continuously moved downwardly, and a plurality of singlecrystal products are continuously formed by intermittently cutting thesingle crystal body being downwardly moved.

The first aspect of the present invention also relates to a singlecrystal product-producing apparatus which includes a singlecrystal-growing device in which a melt of a single crystal raw materialis placed and a single crystal body is grown by drawing downwardly themelt, a moving device for continuously moving downwardly the grownsingle crystal body, and a cutter for intermittently cutting the singlecrystal body being downwardly moved to continuously produce a pluralityof single crystal products.

The present inventors have found out that the single crystal productshaving uniform composition and characteristics as well as a uniformshape can be obtained by continuously pulling downwardly the singlecrystal body and intermittently cutting the single crystal body at agiven downstream location under the pulling down step. The presentinvention has been accomplished based on this finding. Morespecifically, it was found out that the process for continuouslyproducing a plurality of the single crystal products by continuouslypulling downwardly the grown single crystal body and intermittentlycutting the single crystal body being moved is a process forindustrially and stably mass-producing a number of the single crystalproducts having a given shape.

The above moving device preferably includes a pair of rotary bodies forsandwitching the single crystal body therebetween, and a driving devicefor rotating the rotary bodies, wherein the single crystal body iscontinuously downwardly moved by rotating the rotary bodies such thatthe single crystal body is sandwiched between the pair of the rotarybodies. According to this embodiment, an installation space for themoving device can be reduced. Further, since a pressure can be stablyapplied upon the single crystal body even with the lapse of time, thereis no fear that the crystallinity of the single crystal body isdeteriorated upon application of a large stress upon a part of thesingle crystal. This construction is, particularly suitable for pullingdown the single crystal fiber.

In the above embodiment, if the temperature of the single crystal bodyis high, particularly, beyond 200° C., the single crystal body may beadversely affected depending upon the material constituting the rotarybodies. Therefore, it is preferable that the rotary bodies are made of aheat-resistive material such as Teflon. Further, if a seed crystal ispulled downwardly by the above rotary bodies and then the single crystalbody is continuously pulled down, it is difficult to smoothly move aportion of the single crystal body in the vicinity of a interfacebetween the seed crystal and the single crystal body because thedimension of the seed crystal differs from that of the single crystalbody. Therefore, it is preferable to pull downwardly the seed crystal byanother pulling down mechanism exclusively for the seed crystal.

Further, in a preferable embodiment the single crystal-moving deviceincludes a plurality of holders for grasping the single crystal body,and a driving device for vertically moving the holders, wherein thesingle crystal body is grasped by one holder and this holder isdownwardly moved such that the single crystal body is grasped by thisholder, the single crystal body is then grasped by the other holder andthis other holder is downwardly moved such that the single crystal bodyis then grasped by the other holder, and these steps are repeated todownwardly move the single crystal body. According to this construction,even if the dimension and the shape of the single crystal body arechanged variously, such changes can be easily be coped with by adjustinga pair of chucks of each of the holders.

However, in the above embodiment, it may be feared that the singlecrystal body is vibrated or its central axis is deviated due to stressapplied upon the single crystal body at the moment the single crystalbody is grasped by the chucks of the holder. In order to prevent this,it is effective to simultaneously grasp the single crystal at pluralsites. Further, if the single crystal body is grasped by a pair of thechucks such that the center between a pair of the chucks is notcoincident with that of the single crystal body, it may be feared thatthe crystallinity of the single crystal body is deteriorated due tostress applied upon the single crystal body from either one of thechucks. In order to prevent this, the chucks are preferably madedetachable so that the fitted location of each of the chucks may bechanged or adjusted to make the center of a pair of the chuckscoincident with the center of the single crystal body.

Furthermore, according to the present invention, it is necessary toprovide the pulling device for pulling downwardly the single crystalbody. Although a method may be considered that the single crystal bodyis downwardly led by the self weight of the melt inside the crucible,the crystallinity of the single crystal will be deteriorated by such amethod.

In a preferred embodiment, the cutter cuts the single crystal body byfusing through heat-generating a heating wire. This is a method tolocally fuse the single crystal body by instantaneously raising thetemperature of the heater arranged near around an intended portion ofthe single crystal body. This method hardly applies stress upon thesingle crystal body with no fear of adversely affecting thecrystallinity of the single crystal body.

Further, in a preferable embodiment, a cutter for cutting the singlecrystal body by fusing it through irradiating a laser beam upon thesingle crystal body. This method scarcely exerts mechanical forces uponthe single crystal and does not cause deterioration of thecrystallinity. Further, such a cutter can be easily set relative to thesingle crystal body. As the laser, carbon dioxide laser may bepreferably used.

In addition, in a preferred embodiment, the cutter cuts the singlecrystal body by mechanically destructing a given portion thereof throughpressing a cutting member against the single crystal body. For thispurpose, in order to reduce mechanical stress applied to the singlecrystal body, it is preferable to use a shearing member or scissors eachhaving a distal end of a reduced cross-sectional area.

Furthermore, in a preferred embodiment, the single crystal-producingapparatus includes a feeder for automatically supplementing a freshsingle crystal raw material into the melt inside the crucible. In thiscase, the single crystal raw material can be continuously supplementedin the crucible at a given feed rate. Further, a given amount of thesingle crystal raw material can be intermittently fed into the crucibleevery given interval.

The single crystal raw material can be fed according to a given program.The single crystal-producing apparatus preferably includes a device formeasuring the level of the melt in the crucible, and a controller formaintaining the level of the melt in the crucible at a constant heightby controlling the feed rate of the single crystal raw material based ona signal from the measuring device. Although the growing state of thesingle crystal body changes variously, the thermodynamic condition inthe vicinity of the single crystal drawing hole can be kept constant sothat the crystallinity and the composition of the single crystal bodymay be kept constant.

For this purpose, when a thermocouple is arranged as the measuringdevice in the vicinity of the surface of the melt inside the crucible,the temperature detected by the thermocouple decreases as the surface ofthe melt lowers. The controller receives a corresponding signal from thethermocouple, and outputs an order to the raw material feeder so that afresh single crystal raw material may be fed in the crucible. In thisembodiment, if the raw material is fed by a batch system, thecrystallinity may be adversely affected due to reduction in thetemperature of the melt at the moment the raw material is fed.Therefore, it is preferable that while the temperature in the vicinityof the melt is continuously detected by the thermocouple, the rawmaterial is continuously fed at a given rate, and when reduction in thetemperature is detected by the thermocouple, a small amount of the rawmaterial is fed. By so doing, the amount of the raw material to be fedby the batch system can be reduced.

The thermocouple is particularly preferred if the temperature of themelt is higher beyond 800° C.

If the temperature of the melt inside the crucible is relatively low, atemperature sensor or an optical sensor for detecting the surface of themelt by a light beam may be arranged inside the furnace. However, if themelt exceeds 800° C., it may be that such a sensor is placed in a sensorcover, and a cooling medium may be flown inside the sensor cover.

In a preferred embodiment, the single crystal-producing apparatusaccording to the present invention includes a device for measuringchanges in the weight of the melt, and a controller for controlling thefeed rate of the single crystal raw material based on a signal from themeasuring device so that the weight of the melt in the crucible may bekept in a given range. By so doing, the crystallinity of the singlecrystal body can be kept constant similarly as in the above case.

The single crystal-producing apparatus according to the presentinvention preferably includes an observing device (or a shape measuringdevice) for observing the shape of the single crystal body, and a shapecontroller for controlling the shape of the single crystal body based onthe information from the observing device. By so doing, if the shape ofthe single crystal body changes during the automatic mass-production ofthe single crystal products, such changes can be corrected. Morespecifically, if the dimension of the single crystal body increases,such a dimensional change amount is detected, and a signal correspondingto this change amount is fed to the controller. The controller mayoutput a temperature control signal to the heater inside the furnace sothat the dimension of the single crystal body may be slightly reduced bysending a signal from the controller to the heater to make the heater toslightly raise the temperature. If the heater receives a signal from thecontroller to slightly lower the temperature, the dimension of thesingle crystal body can be slightly increased.

The shape measuring device may be a device for monitoring the outershape of the single crystal body through taking a view of this outershape with a CCD camera. However, since this device cannot detect anabsolute actual dimension of the single crystal body, it is preferableto set a standard scale near the single crystal body. Further, the viewof the single crystal body may be dark, it is preferable to set anilluminating device near the single crystal body.

In addition, the dimension of the single crystal body may be measured byirradiating a laser beam upon the single crystal body. In this case, itis necessary that the temperature in the vicinity of the laser beamsource is lowered by setting the laser beam source away from the furnacebody. If the laser beam is irradiated upon the single crystal body fromone direction only, the dimension can be measured only from this onedirection so that the entire shape thereof cannot be measured.Therefore, preferably the dimension of the single crystal body ismeasured by irradiating the laser beams from at least two crossingdirections.

Further, if a line sensor is used, its viewing image is unfavorablydark. In this case, it is also preferable to set an illuminating devicefor the single crystal body.

In a preferred embodiment, the single crystal-producing apparatusincludes an observing device for observing the material quality of thesingle crystal body, and a quality controller for controlling thematerial quality of the single crystal body based on information fromthe observing device. By so doing, the single crystal products havinguniform crystallinity can be mass-produced. In this embodiment, it ispreferable that a laser beam is irradiated upon the single crystal bodybeing pulled down, an outputted light beam from the oxide-series singlecrystal body is measured, and the proportion ratio of components in thecomposition of the single crystal raw material to be fed to the crucibleis controlled based on the measuremental result so that change in thecomposition of the raw material may be prevented even in the case ofcontinuously pulling down a single crystal fiber.

More specifically, if the peak wavelength of a generated light beam fromthe oxide-series single crystal shifts to a shorter wavelength side,this means that the composition of the single crystal deviates from atarget one. Therefore, the proportion ratio of components in thecomposition of the raw material is changed so that the shifting of thepeak wavelength may be reduced. By so doing, while the single crystalfiber or the like is being drawn, its composition can be maintained in agiven range. It is more preferable that half wavelength light beams aredetected through irradiating a laser beam on an oxide-series singlecrystal having a SHG effect.

Further, in a preferred embodiment, the invention apparatus includes atransfer device for automatically arraying and transferring the cutsingle crystal bodies. This is preferable from the standpoint of themass-production, because the arrayed single crystal products can beautomatically transferred to a succeeding step. Particularly, when thesingle crystal fiber product is used as an SHG element, the aboveembodiment is extremely preferable, because such single crystal fiberproducts are transferred to a succeeding assembling step as they arearrayed.

Further, according to a preferred embodiment, a plurality of singlecrystal drawing holes are provided in the single crystal growing deviceso that single crystal bodies may be simultaneously pulled down throughsaid plural single crystal drawing holes, respectively.

As single crystals to which the present invention can be applied,oxide-series single crystals and non-oxide series single crystals may berecited. Particularly, the oxide-series single crystals are preferred.As such oxide-series single crystals, known oxide-series single crystalsmay be recited, and particularly oxide-series single crystals for bluelaser device by SHG, such as KLN, KLTN and KN (KNbO₃) as well asoxide-series single crystals for ultraviolet laser device, such as CLBO(Cs₀.5 Li₀.5 B₃ O₅), BBO (β-BaB₂ O₄) and LBO (LIB₃ O₅) are preferred.Further, later described oxide-series single crystals in a state ofsolid solution are preferred.

Next, a preferred growing device used in the present invention will beexplained. The present inventors have made studies on how to enlarge thecrucible so as to establish the oxide-series single crystalmass-production technique based on μ pulling down process. During theprocess of these studies, the inventors have tried to enlarge thecrucible, provide a nozzle portion extending downwardly from thecrucible, providing a single crystal-growing section at the lower end ofthe nozzle portion, and independently control the respectivetemperatures of the crucible and the single crystal-growing section.

As a result, it was discovered leading to the present invention thateven if a large amount such as not less than 5 g of the powdery rawmaterial to be melted in the crucible is used and the volume of thecrucible is correspondingly increased, the oxide-series single crystalbody can be easily continuously pulled down.

The reason why the above function and effect are obtained is probablythat the provision of the single crystal-growing section at the lowerend of the nozzle portion makes the single crystal-growing sectiondifficult to be directly influenced by the heat generated by the melt inthe crucible, and the temperature gradient in the vicinity of the singlecrystal-growing section can be made greater by simultaneously andindependently controlling the temperatures of the single crystal-growingsection, the end of nozzle portion, and the crucible.

In addition, the inventors have found out that according to the abovetechnique, even if the amount of the powdery raw material to be meltedin the crucible is increased up to around 30-50 g, changes in thecomposition in the case of KLN single crystal fiber products issuppressed to a surprisingly high accuracy with changes of not more than0.01 mol %. Therefore, the oxide-series single crystal having anextremely high accuracy composition can be mass-produced byincorporating the above technique into the present invention.

Further, the present inventors have studied the state of the melt in thesingle crystal-growing section as well as the physical properties of thesingle crystal by using the above producing apparatus. As a result, itwas discovered that if the surface tension is more dominant than thegravity in the environment of the single crystal-growing section, theoxide-series single crystal body having a very small change incomposition can be excellently pulled down continuously. It isconsidered that a good solid phase/liquid phase interface (meniscus) isformed by so doing.

In order to produce the condition that the surface tension is moredominant than the gravity in the environment of the singlecrystal-growing section, it is effective to provide, inside thecrucible, a mechanism for reducing the gravity acting on the melt in thenozzle. The inventors have investigated such a mechanism and found outthat the condition that the surface tension is more dominant than thegravity acting on the melt can be realized particularly by setting theinner diameter of the nozzle portion to not more than 0.5 mm so that auniform meniscus can be formed at the distal end opening of the nozzleportion.

In this case, if the inner diameter of the nozzle portion is less than0.01 mm, the growing speed of the single crystal becomes too small.Therefore, the inner diameter of the nozzle portion is preferably notless than 0.01 mm from the viewpoint of mass production. The optimuminner diameter of the nozzle portion is preferably set in a range of0.01 to 0.5 mm from the stand point of the mass production, which mayslightly change depending on the viscosity, the surface tension, and thespecific gravity of the melt, the growing speed of the single crystal,etc.

Further, the present inventors have studied the above point, andobtained the following finding. That is, it was considered that thesingle crystal fiber could be continuously pulled down in theconventional μ pulling down process since the scale of the crucible wassmall. It can be presumed that since the amount of the melt in thecrucible was small, the melt was attached to the surface of the wall ofthe crucible due to its surface tension, and therefore the gravityacting on the drawing hole was relatively smaller, a somewhat uniformsolid phase/liquid phase interface was formed. However, it is presumedthat as the dimension of the crucible was increased, the condition thatthe surface tension was more dominant in the vicinity of the drawinghole was disappeared.

In the above process, the temperature gradient can be easily made largerin the vicinity of the single crystal-growing section as viewed in thelongitudinal direction of the nozzle portion. Owing to this, the meltflowed down through the nozzle portion can be rapidly cooled.

Therefore, this producing process is suitable particularly for theproduction of the single crystal of a solid solution state. The singlecrystal of a solid solution state has the property that the proportionratio in the composition changes under an equilibrium condition. Whenthe conventional μ pulling down process is used, the equilibriumcondition exists in the vicinity of the drawing hole, and thecomposition of the solid solution is changed depending on changes in thetemperature or change in the solidifying rate. This is considered to becaused by the above change in the proportion ratio in the composition.To the contrary, according to the invention process and apparatus, sincethe single crystal can be rapidly cooled in the vicinity of the singlecrystal-growing section, the composition of the melt can be maintained.

As the solid solution, for example, KLN, KLTN K₃ Li_(2-2x) (Ta_(y)Nb_(1-y))_(5+x) ! O_(15+x) and Ba_(1-x) Sr_(x) Nb₂ O₆, which havetungsten-bronze structre, and Mn-Zn ferrite may be recited.

When the raw material is fed into the crucible and melted therein, thethermal condition inside the crucible changes due to heat of dissolutionof the raw material, so that the composition of the single crystalchanges. However, if the nozzle portion is provided below the crucibleas mentioned before, the raw material can be continuously orintermittently fed in the crucible. For, even if the thermal changeoccur inside the crucible, thermal influence upon the singlecrystal-growing section is small. Since the single crystal is not in anequilibrium state at the single crystal-growing section but in akinetics state, the single crystal-growing section is further hardlyinfluenced by the thermal changes.

The producing apparatus according to the present invention is notlimited to any particular heating means for the crucible. However, it ispreferable to provide a heating furnace as surrounding the crucible. Inthis case, it is preferable that the heating furnace is divided into anupper furnace portion and a lower furnace portion, and the crucible issurrounded by the upper furnace portion, and the upper furnace portionmay be heated at a higher temperature to assist the melting of thepowder inside crucible. On the other hand, it is preferable that thelower furnace portion is arranged to surround the nozzle portion, andthe temperature of the lower furnace portion is set lower so that thetemperature gradient in the single crystal-growing section at the lowerend of the nozzle portion may be greater.

Further, in order to improve the efficiency of melting the powder insidethe crucible, it is preferable that the crucible itself is made of anelectrically conductive material, and is caused to generate heat throughapplying electric power thereto rather than heating the crucible byusing only the heating furnace outside the crucible. Further, in orderto keep the molten state of the melt flowing the nozzle portion,preferably the nozzle is made of a conductive material and caused togenerate heat through applying electric power to the nozzle portion.

In order to make larger the temperature gradient particularly in thesingle crystal-growing section, it is preferable that a current-passingmechanism for the crucible and that for the nozzle portion areseparately provided, and can be independently controlled.

As the above conductive material, materials such as platinum,platinum-gold alloys, platinum-rhodium alloys, platinum-iridium alloys,and iridium are preferred.

The present invention can excellently be applied to not only theproduction of the single crystal fiber products but also the productionof the planar shaped single crystal products. A specific process for theformation of such a planar shaped single crystals will be explainedlater.

The KLN single crystal has recently attracted attention as one ofoptical materials, and particularly the KLN single crystal has recentlyattracted attention as a single crystal for a blue laser device bysecond harmonic generation (SHG) element. Since the KLN single crystalcan generate a light beam in an ultraviolet ray area of down to 390 mn,such a single crystal can find wide applications in optical disc memory,medical use, photochemical use, various optical measurements, etc. byutilizing the short wavelength light beam as mentioned above. Further,since the KLN single crystal has a large electro-optic effect, it can beapplied to an optical memory element utilizing a photo-refractive effectthereof.

According to the oxide-series single crystal producing process accordingto the second aspect of the present invention, the raw material for theoxide-series single crystal is melted in the crucible, a seed crystal isbrought into contact with the melt, and the oxide-series single crystalbody is grown, while drawing the melt downwardly. This process iscarried out by using the producing apparatus including the crucible, thenozzle portion extending downwardly from the crucible, and thedownwardly directed single crystal-growing section at the distal end ofthe nozzle portion, wherein the temperature of the crucible and that ofthe single crystal-growing section are independently controlled.

Further, the oxide-series single crystal producing apparatus accordingto the second aspect of the present invention is adapted to melt theoxide-series single crystal raw material in the crucible, bringing aseed crystal into contact with the melt, and growing the oxide-seriessingle crystal, while drawing the melt downwardly. This apparatusincludes the crucible, the nozzle portion extending downwardly from thecrucible, the single crystal-growing section provided at the lower endof the nozzle portion, and the mechanism for independently controllingthe temperature of the crucible and that of the single crystal-growingsection.

When the drawing hole is provided in the bottom of the crucible as inthe conventional apparatus and the melt is directly drawn through thedrawing hole, it is considered that a good solid phase/liquid phaseinterface could not be formed in the vicinity of the drawing hole due tothermal influence of the crucible and the melt in the crucible in thevicinity of the drawing opening.

In addition, the present invention is not limited solely to the meltingof a large amount of the powder and the continuous pulling down of thesingle crystal body through the lower end of the nozzle portion. Thepresent inventors continuously pulled down a KLN single crystal fiber byusing a conventional single crystal-producing apparatus, while theamount of the powder inside the crucible was suppressed to 300 to 500 mgthen precisely measured the composition of the fiber. As a result, itwas discovered that the composition changed in a range of about 1.0 mol%.

Surprisingly high accuracy can be realized by the producing process andapparatus according to the second aspect of the prevent invention fromthe stand point of the improved homogeneity of the composition of thesingle crystal as compared with the conventional pulling down process.

Further, for the above-mentioned reason, an oxide series single crystalhaving a segregation composition can be produced. For example, whenneodymium is added or substituted in LiNbO₃, neodymium only in an amountsmaller than that in the composition of the melt enters the singlecrystal because the segregation coefficient of neodium is not 1.0. Forexample, even if about 1.0 mol % of neodymium is contained in the melt,only about 0.3 mol % of neodymium can be substituted in the singlecrystal. However, according to the present invention, the single crystalhaving the same composition as that of the melt can be produced byrapidly cooling the melt inside the nozzle portion as mentioned above,without segregation. This can be also applied to other laser singlecrystals such as YAG (Y₃ Fe₅ O₁₂) partially substituted by Nd, Er and/orYb, and YVO₄ partially substituted by Nd, Er and/or Yb.

The present inventors has proceeded their investigations, and obtainedthe following finding. That is, nozzle portions having various innerdiameters were produced by platinum, and single crystals made of KLN,etc. were actually experimentally grown. As a result, when an amount ofthe melt inside the crucible was large, the melt dripped from a distalend face of the nozzle portion, and consequently it was difficult togrow a fiber or the like in some cases. For example, when the surfacelevel of the melt measured from the bottom of the crucible was set atnot less than 30 mm or not less than 50 mm, the melt dripped from thedistal end face of the nozzle portion even when the inner diameter ofthe nozzle portion was reduced to 0.2-0.5 mm.

In order that although the amount of the raw material received in thecrucible is particularly increased like this, the oxide-series singlecrystal may be stably mass-produced, a nozzle portion is provided at aside face of the crucible, and a part of the nozzle portion is laidabove a joined portion between the crucible and the nozzle portion. Inorder to most stably pull down the oxide-series single crystal, theheight of the distal end face of the nozzle portion is made differentfrom the height of the upper surface of the melt by a given value in theabove construction.

How to make the height of the distal end face of the nozzle portiondifferent from that of the upper surface of the melt so as to obtain anoptimum growing condition depends upon numerous factors such as thephysical properties (viscosity, melting point, etc.) of the singlecrystal, the structure of the furnace body (temperature distribution,etc.), the structure of the crucible (the shape of the melting section(the section for melting the raw material) of the crucible, and theshape of the nozzle portion), the growing temperature, the temperaturegradient of the single crystal-growing section, etc. However, if theabove difference is increased, the growing speed becomes greater,whereas if the difference is decreased, the melt at the distal end faceof the nozzle portion is less influenced by the gravity acting upon thismelt so that the melt may be difficult to drip. For this reason, if theheight of the nozzle portion is taken as "zero mm", it is preferable toset the surface level of the melt inside the crucible to not less than-10 mm but not more than 50 mm. If the surface level of the melt insidethe crucible is set to not more than 50 mm, the above-mentioned growingstate can be more easily controlled. On the other hand, even if thedistal end face of the nozzle is located higher than the upper surfaceof the melt in the crucible but by not more than 10 mm, the melt iscontinuously fed to the nozzle portion due to the capillary phenomenoninside the nozzle. The distal end face of the nozzle portion can be setto a location lower than a bottom surface of the melt inside thecrucible.

In the above embodiment, the invention apparatus may further include aheat-insulating wall for adiabatically separating a melting furnace inwhich the crucible is placed from a growing furnace in which the singlecrystal-growing section is placed, wherein the nozzle portion isinserted through a through-hole provided in the heat-insulating wall. Byso doing, the melt can be obtained inside the crucible by heating at asufficiently high temperature, whereas temperature difference betweenthe single crystal-growing section and the melt in the crucible canarbitrarily be controlled so that the melt flowing through the nozzleportion may be rapidly cooled in the single crystal-growing section.

The producing apparatus according to the second aspect of the presentinvention is not limited to any particular heating means for thecrucible. However, it is preferable to provide a heating furnace assurrounding the crucible. In the case that the nozzle portion isextended downwardly below the crucible, it is preferable that theheating furnace is divided into an upper furnace portion and a lowerfurnace portion, and the crucible is surrounded by the upper furnaceportion so that the upper furnace portion may be heated to a highertemperature to assist melting of the powder in the crucible. On theother hand, it is preferable that the lower furnace portion is arrangedto surround the nozzle portion, and the temperature of the lower furnaceportion is set lower so that the temperature gradient in the singlecrystal-growing section at the lower end of the nozzle portion may begreater.

Further, in order to improve the efficiency of melting the powder insidethe crucible, preferably the crucible itself is made of a conductivematerial, and is caused to generate heat through applying electric powerthereto, rather than heating the crucible by using only the heatingfurnace outside the crucible. Further, in order to keep the molten stateof the melt flowing through the nozzle portion, preferably the nozzle ismade of a conductive material, and caused to generate heat throughapplying the electric power thereto. The respective temperatures of thenozzle portion and the crucible portion may be controlled by heatingwith radio frequency waves.

In order to make larger the temperature gradient particularly in thesingle crystal-growing section, preferably a current-passing mechanismfor the crucible and that for the nozzle portion are separatelyprovided, and can be independently controlled.

As the above conductive material, materials such as platinum,platinum-gold alloys, platinum-rhodium alloys, platinum-iridium alloys,and iridium are preferred.

Since the corrosion-resistant metals such as platinum all haverelatively small resistivities, the resistance of the nozzle portionneeds to be increased to some degree by decreasing the thickness of thenozzle portion so that the nozzle portion may effectively beheat-generated. For example, when the nozzle portion was made ofplatinum, it needed to be formed by a thin film of about 100-200 μm.However, if the nozzle portion is formed by such a thin film, it isstructurally weak, so that stable production of the single crystal bodymay be difficult due to deformation of the nozzle portion in some case.

Under the circumstances, the nozzle portion may be surrounded by aheat-generating resistive member, which can be caused to generate heatthrough feeding electric power thereto. In this case, the nozzle portionmay be made of the above corrosion-resistant metal, and this metal isalso caused to generate heat through feeding electric power thereto. Inthis case, no electric power may be applied to the nozzle portion. Inthe above case, a principal heating function may be given to theheat-generating resistive member surrounding the nozzle portion, so thata heat-generating load required for the nozzle portion becomes smaller.Since the nozzle portion may not necessarily be caused to generate heat,the mechanical strength of the nozzle portion can be enhanced bythickening the nozzle portion (for example, to not less than 300 μm),which makes the apparatus more suitable for the mass-production.

According to the producing apparatus of the second aspect of the presentinvention, the raw material can be continuously or intermittently fedinto the crucible. For, if the raw material is supplied in the crucible,the state thermally changes inside the crucible due to the heat of thedissolution of the raw material, and the composition of the singlecrystal correspondingly changes. However, according to the inventionproducing apparatus, even if such thermal change occurred inside thecrucible, the single crystal-growing section is less thermallyinfluenced. Further, since the single crystal-growing section is not inan equilibrium state but in a kinetics state, the growing section isstill less thermally influenced.

The second aspect of the present invention can be excellently applied tonot only to the production of the single crystal fiber products but alsothe planar single crystal products. A concrete process of producing suchplanar single crystal products will be explained later.

The oxide-series single crystal producing process according to the thirdaspect of the present invention includes the steps of melting anoxide-series single crystal raw material in a melting crucible,continuously feeding the melted raw material to a single crystal-growingcrucible having a volume smaller than that of the melting crucible (thecrucible for melting the raw material) through an opening of the meltingcrucible, contacting a seed crystal with the melt at a drawing hole ofthe single crystal-growing crucible (the crucible for growing the singlecrystal), and growing the oxide-series single crystal body while drawingdown the melt through the drawing hole.

The third aspect of the present invention also relates to the producingapparatus for contacting the seed crystal with the melt at the drawinghole of the crucible and growing the oxide-series single crystal, whiledrawing down this melt through the drawing hole, and the apparatusincludes the melting crucible for melting the oxide-series singlecrystal raw material and having the opening, the single crystal-growingcrucible having the volume smaller than that of the melting crucible andprovided with the drawing opening, wherein the raw material melted inthe melting crucible is continuously fed to the single crystal-growingcrucible through the opening of the melting crucible, the seed crystalis contacted with the melt at a drawing hole of the singlecrystal-growing crucible, and the oxide-series single crystal body isgrown while pulling down the melt through the drawing hole.

The present inventors have continued studies to enlarge the crucible soas to establish the oxide-series single crystal mass-productiontechnique based on the μ pulling down process. However, it was revealedthat since the enlargement of the crucible made it impossible to drawthe single crystal fiber through the drawing hole, it was difficult tofind a solution for the above enlargement problem. Having investigatedcauses therefor, the inventors found that if a system in which thedrawing hole was provided in the bottom of the crucible and the melt wasdirectly drawn through the drawing hole was employed and the heatcapacity of the crucible and the melt increased beyond a given level, agood solid phase/liquid phase interface could not be formed in thevicinity of the drawing hole by the thermal influence of the crucibleand the melt upon the vicinity of the drawing hole.

Irrespective of the above finding, the inventors have looked for anyprocess of continuously treating a large amount of the raw material forcontinuously pulling the single crystal fiber. During the process of theinvestigation, the inventors have found a technique that the singlecrystal-growing crucible having the volume smaller than that of themelting crucible is separately provided from this melting crucible, thesingle crystal raw material is melted in the melting crucible, themelted raw material is continuously fed to the single crystal-growingcrucible through the opening of the melting crucible, a single crystalis contacted with the melt at the drawing opening of the singlecrystal-growing crucible, and the oxide-series single crystal is grownwhile drawing the melt downwardly.

As a result, the inventors found a finding leading to the third aspectof the present invention, that even if the amount of the powdery rawmaterial to be melted in the melting crucible was increased to not lessthan 5 g and the volume of the melting crucible was correspondinglyincreased, the oxide-series single crystal could be easily continuouslypulled down.

In addition, the third aspect of the present invention is not merelylimited to the advantage that the single crystal fiber can becontinuously pulled down through melting a large amount of the powder.The present inventors continuously pulled down a KLN single crystalfiber by using the conventional single crystal producing apparatus,while the amount of the powdery raw material in the crucible wassuppressed to around 300-500 mg. The precise measurement of thecomposition of the thus obtained single crystal fiber revealed that thecomposition varied within about 1.0 mol %.

To the contrary, according to the third aspect of the present invention,even if the amount of the powdery raw material to be melted in thecrucible was increased to around 30-50 g and the melt was continuouslyfed to the single crystal-growing crucible such that the amount of themelt in the growing crucible may reach around 300-500 mg, changes in thecomposition in the case of KLN single crystal fiber products weresuppressed to lower values of indeed not more than 0.01 mol % showing asurprisingly high accuracy. Thus, according to the producing process andapparatus of the third aspect of the present invention, surprisinglyhigh accuracy can be realized in that the homogeneity of the compositionof the single crystal is improved, as compared with the conventional μpulling down process.

The reason for the above is not clear. However, according to theconventional producing apparatus based on the μ pulling down process,the powdery raw material was fed and melted in the crucible, and thesingle crystal fiber was pulled down through the drawing hole of thecrucible. Therefore, the temperature of the melting crucible and that ofthe melt therein have to be kept high so that the melt might not besolidified in the vicinity of the drawing hole, and therefore it wasdifficult to maintain the temperature condition and the temperaturegradient such that the solid crystal might be solidified at a singlecrystal-growing point in the vicinity of the drawing hole. From thisreason, it is considered that even if a single crystal fiber couldhappened to be pulled down under a certain condition, the compositionthereof unavoidably suffered changes.

To the contrary, according to the third aspect of the present invention,since the raw material was melted in the melting crucible and then themelt is fed from the melting crucible to the single crystal-growingcrucible, the single crystal-growing crucible is not thermallyinfluenced by the high temperature of the melting crucible. Therefore,the temperature condition in the vicinity of the drawing hole of thesingle crystal-growing crucible can be independently set separately fromthat of the melting crucible. As a result, good single crystal body canbe drawn out by setting a greater temperature gradient at the singlecrystal-growing point in the vicinity of the drawing hole of the singlecrystal-growing crucible.

For that purpose, it is preferable to independently heat the meltingcrucible and the single crystal-growing crucible by separate heatingmechanisms. Further, it is preferable to largely separate the meltingcrucible from the single crystal-growing crucible. For this, it ispreferable that a nozzle portion is extended downwardly from the bottomof the melting crucible, the raw material melted in the melting crucibleis continuously fed to the single crystal-growing crucible through thenozzle portion.

In the third aspect of the present invention, the raw material is meltedin the melting crucible, and the melt is continuously fed to the singlecrystal-growing crucible. It is preferable that the raw material is keptmelted when the raw material from the melting crucible is brought intocontact with the melt in the single crystal-growing crucible. However,the melt may be solidified after it is discharged through the opening ofthe melting crucible. In this case, it is preferable that the solidifiedmaterial in the vicinity of the opening is continuously pulleddownwardly or the material solidified in the vicinity of the opening ismelted instantaneously after it is contacted with the melt in the singlecrystal-growing crucible so that the solidified raw material might notclog the opening.

On the other hand, the present inventors have studied the relationshipbetween the state of the melt in the single crystal-growing crucible andthe physical properties of the single crystal, by using the aboveproducing apparatus. As a result, the inventors have discovered that ifthe surface tension is more dominant than the gravity in the environmentof the single crystal-growing section, the good single crystal havingextremely small changes in composition can be continuously pulled down.The reason therefor is considered that a good solid phase/liquid phaseinterface can be formed in this case.

Further, the present inventors have made researches on the above reasonto find out the following finding. That is, it is considered that sincethe scale of the crucible in the conventional μ pulling down process wassmall, the single crystal fiber could be continuously pulled down. Thisis considered since the amount of the melt inside the crucible wassmall, the melt was adhered to the surface of the inner wall of thecrucible through its surface tension to make the gravity acting on thedrawing opening relatively small, and a solid phase/liquid phaseinterface which was homogeneous to some extent could be formed. However,it is considered that if the dimension of the crucible is increased,such condition that the surface tension is more dominant in the vicinityof the drawing opening was disappeared.

Further, according to the third aspect of the present invention, it iseasy to make larger the temperature gradient in the vicinity of thesingle crystal-growing point for the single crystal-growing crucible. Byso doing, the melt can be rapidly cooled.

Therefore, the third aspect of the present invention is particularlysuitable for the production of the single crystal of a solid solutionstate. The single crystal of a solid solution state has a tendency thatits composition ratio changes under an equilibrium condition. When theconventional μ pulling down process is employed, the equilibriumcondition exists in the vicinity of the drawing hole so that thecomposition of the solid solution changes due to a slight temperaturechange or slight changes in the solidifying speed. To the contrary,according to the method and apparatus of the third aspect of the presentinvention, since the area near the single crystal-growing section can berapidly cooled, the composition of the melt can be kept constant.

As the solid solution, for example, KLN, KLTN K₃ Li_(2-2x) (Ta_(y)Nb_(1-y))_(5+x) !O_(15+x) and Ba_(1-x) Sr_(x) Nb₂ O₆, which havetungsten-bronze structure, and Mn-Zn ferrite may be recited.

Further, for the above-mentioned reason, an oxide series single crystalhaving a segregation composition can be produced. For example, whenneodymium is added or substituted in LiNbO₃, neodymium only in an amountsmaller than that in the composition of the melt enters the singlecrystal because the segregation coefficient of neodium is not 1.0. Forexample, even if about 1.0 mol % of neodymium is contained in the melt,only about 0.3 mol % of neodymium can be substituted in the singlecrystal. However, according to the present invention, the single crystalhaving the same composition as that of the melt can be produced byrapidly cooling the melt inside the nozzle portion as mentioned above,without segregation. This can be also applied to other laser singlecrystals such as YAG (Y₃ Fe₅ O₁₂) partially substituted by Nd, Er and/orYb, and YVO₄ partially substituted by Nd, Er and/or Yb.

The producing apparatus according to the present invention is notlimited to any particular heating means for the crucibles. However, itis preferable to provide a heating furnace as surrounding the crucible.In this case, it is preferable that the heating furnace is divided intoan upper furnace portion and a lower furnace portion, and the meltingcrucible is surrounded by the upper furnace portion so that the upperfurnace portion may be heated at a higher temperature to assist meltingof the material powder inside the melting crucible.

On the other hand, it is preferable that the lower furnace portion isarranged to surround the single crystal-growing crucible., and thetemperature of the lower furnace portion is set lower so that thetemperature gradient in the single crystal-growing section of the singlecrystal-growing crucible may be greater.

Further, in order to improve the efficiency of melting the powdermaterial inside the melting crucible, it is preferable that the meltingcrucible itself is made of a conductive material, and is caused togenerate heat through applying electric power thereto, rather thanheating the melting crucible by using only the heating furnace outsidethe melting crucible.

Further, in order to keep the molten state of the melt flowing thenozzle portion of the melting crucible, it is preferable that the nozzleportion is made of a conductive material, and caused to generate heatthrough applying the electric power to the nozzle portion. Further, itis preferable that a radio frequency heating mechanism is provided toheat the melting crucible body and the nozzle portion through radiofrequency induction heating.

As the above conductive material, materials such as platinum,platinum-gold alloys, platinum-rhodium alloys, platinum-iridium alloys,and iridium is preferred.

Since the corrosion-resistant metals such as platinum all haverelatively small resistivities, the resistance of the nozzle portionhave to be increased to some degree by decreasing the thickness of thenozzle portion so that the nozzle portion may be effectivelyheat-generated. For example, when the nozzle portion was made ofplatinum, it had to be formed by a thin film of about 100-200 μm.However, if the nozzle is formed by such a thin film, it is structurallyweak, so that stable production of the single crystal body may bedifficult due to deformation of the nozzle portion in some case.

Under the circumstances, the nozzle portion may be surrounded by aheat-generating resistive member, which can be caused to generate heatthrough feeding electric power thereto. In this case, the nozzle portionmay be made of the above corrosion-resistant metal, and this metal mayalso be caused to generate heat through feeding electric power thereto.In this case, no electric power may be applied to the nozzle portion. Inthe above case, a principal heating function may be given to theheat-generating resistive member surrounding the nozzle portion, so thata heat-generating load required for the nozzle portion becomes smaller.Since the nozzle portion may not necessarily be caused to generate heat,the mechanical strength of the nozzle portion can be enhanced bythickening the nozzle portion (for example, to not less than 300 μm),which makes the apparatus more suitable for the mass-production.

According to the producing apparatus of the third aspect of the presentinvention, the raw material can be continuously or intermittently fedinto the melting crucible. For, the state thermally changes inside themelting crucible due to the heat of the dissolution of the raw material,and the composition of the single crystal correspondingly changes.However, according to the invention producing apparatus, even if suchthermal change occurred inside the melting crucible, the singlecrystal-growing crucible is less thermally influenced. Further, sincethe single crystal-growing section of the single crystal-growingcrucible is not in an equilibrium state but in a kinetics state, thegrowing section is still less thermally influenced.

The third aspect of the present invention can be excellently applied tonot only to the production of the single crystal fiber products but alsothe planar single crystal products. A concrete process of producing suchplanar single crystal products will be explained later.

The process according to the fourth aspect of the present inventionincludes the steps of feeding the oxide-series single crystal rawmaterial to the crucible, melting it therein and growing theoxide-series single crystal after a seed crystal is contacted with themelt, wherein a laser beam is irradiated upon the oxide-series singlecrystal, a light outputted from the oxide-series single crystal ismeasured, and the composition ratio of the raw material to be fed to thecrucible is controlled based on the measuremental result.

The oxide-series single crystal-producing apparatus according to thefourth aspect of the present invention is adapted for feeding theoxide-series single crystal raw material to the crucible, melting ittherein and growing the oxide-series single crystal after a seed crystalis contacted with the melt, and includes the crucible with the singlecrystal-drawing hole, a raw material feeder for feeding the raw materialto the crucible, a driving device for pulling down the oxide-seriessingle crystal body from the crucible, a laser beam source forirradiating the laser beam upon the oxide-series single crystal body, ameasuring device for measuring an output light from the oxide-seriessingle crystal body, and a controller for controlling the compositionratio of the raw material to be fed to the crucible based on an outputsignal from the measuring device.

The present inventors have excellently succeeded in solving theabove-mentioned problems, continuously pulling down the single crystalfiber and keeping the composition thereof constant by employing theconstruction according to the fourth aspect of the present invention.More specifically, the inventors discovered that the feeder is providedto feed the oxide-series single crystal raw material to the crucible,the laser beam is irradiated upon the oxide-series single crystal bodybeing downwardly pulled, the output light beam from the oxide-seriessingle crystal is measured, and the composition ratio of the rawmaterial to be fed to the crucible is controlled based on themeasuremental result, whereby even if the single crystal fiber or thelike is continuously pulled down, the composition of the single crystalfiber can be prevented from changing.

Referring to the above in more detail, that the wavelength of a peak ofthe output light beam from the oxide-series single crystal shifts to along wavelength side or a short wavelength side means that thecomposition is deviated from a target one. In that case, the compositionratio of the raw material is changed to reduce the shifting of the peakwavelength. By so doing, the composition of the single crystal fiber canbe kept in a given range, while pulling it down.

These and other objects, features and advantages of the invention willbe appreciated upon reading the following description of the inventionwhen taken in conjunction with the attached drawings, with theunderstanding that some modifications, variations and changes could beeasily made by the skilled person in the art to which the inventionpertains.

BRIEF DESCRIPTION OF THE INVENTION

For a better understanding of the invention, reference is made to theattached drawings, wherein:

FIG. 1 is a block diagram for schematically illustrating an embodimentof the single crystal-producing apparatus according to the first aspectof the present invention;

FIG. 2 is a sectional view of outlining a single crystal-growing deviceto be favorably used in the first aspect of the present invention;

FIG. 3(a) is a sectional view for illustrating a state of the growingdevice in FIG. 2 before a seed crystal is contacted with a melt;

FIG. 3(b) is a sectional view for illustrating a state of the growingdevice in FIG. 2 in which the seed crystal is contacted with the melt;

FIG. 4(a) is a plane view of a plane plate 31 with grooves 32;

FIG. 4(b) is a perspective view of a nozzle portion 35 formed bycombining a pair of the plane plates 31;

FIG. 4(c) is a perspective view for illustrating a state in which asingle crystal plate 36 is being grown through the nozzle portion 35 ofa crucible 37;

FIG. 5 is a view for schematically illustrating a crucible provided withplural rows of nozzle portions;

FIG. 6 is a perspective view for illustrating a moving device and acutter to be favorably used in the first aspect of the presentinvention;

FIG. 7 is a side view for illustrating a principal portion of the movingdevice and the cutter in FIG. 6;

FIG. 8 is a front view of a holder in FIGS. 6 and 7;

FIG. 9 is a side view for outlining another moving device and anothercutter to be favorably used in the first aspect of the presentinvention;

FIG. 10 is a perspective view for illustrating a driving mechanism forrotary bodies used in the moving device in FIG. 9;

FIG. 11(a) is a schematic view for illustrating a state in which aheater 69 is contacted with a single crystal body 12;

FIG. 11(b) is a schematic view for illustrating a state in which thesingle crystal body 12 is cut by the heater 69;

FIG. 12(a) is a front view for illustrating a state in which images ofthe single crystal body 12 and a scale 62 are taken in a monitor 7;

FIG. 12(b) is a perspective view for illustrating a state in which laserbeams 64 and 65 are irradiated upon a single crystal body 63;

FIG. 13 is a sectional view for outlining a single crystal-growingdevice according to an embodiment of the second aspect of the presentinvention;

FIG. 14 is a sectional view for outlining a single crystal-growingdevice according to another embodiment of the second aspect of thepresent invention;

FIG. 15 is a sectional view for outlining a crucible and an electricpower feeding mechanism in a single crystal-producing apparatusaccording to a further embodiment of the second aspect of the presentinvention;

FIG. 16 is a sectional view for structurally outlining a crucible and anelectric power feeding mechanism in a still further embodiment of thesingle crystal-producing apparatus according to the second aspect of thepresent invention;

FIG. 17 is a sectional view for outlining the construction of a cruciblein a still further embodiment of the single crystal-producing apparatusaccording to the second aspect of the present invention;

FIG. 18(a) is a plane view of a flat plate 78 made of acorrosion-resistant material;

FIG. 18(b) is a plane view for illustrating a state in which a groove 79is formed at the flat plate 78;

FIG. 18(c) is a section a view of a nozzle portion 80 formed by joininga pair of the flat plates 78;

FIG. 18(d) is a sectional view illustrating a state in which the nozzleportion 80 is fitted to a crucible 82;

FIG. 19 is a perspective view for illustrating a cut nozzle portion 83constituted by a plurality of tubular members 85;

FIG. 20 is a sectional view for outlining a nozzle portion 89 having anouter diameter-enlarged portion 91 and a crucible;

FIG. 21 is a sectional view for outlining a crucible provided with anozzle portion having a diameter enlarged portion with numerous flowholes;

FIG. 22 is a sectional view for outlining a single crystal-producingapparatus according to a still further embodiment of the second aspectof the present invention;

FIG. 23 is a plane view for outlining the apparatus in FIG. 22;

FIG. 24 is a sectional view of another nozzle portion used in the singlecrystal-producing apparatus in FIGS. 22 and 23 as viewed from athrough-hole 98a;

FIG. 25 is a sectional view for outlining a single crystal-producingapparatus according to an embodiment of the third aspect of the presentinvention;

FIG. 26 is a sectional view for outlining a single crystal-growingcrucible 115 and its adjacent portion;

FIGS. 27(a) and 27(b) are schematic views for illustrating states of adistal end portion of the single crystal-growing crucible 115;

FIG. 28 is a sectional view for outlining the construction of a cruciblein a single crystal-producing apparatus according to the third aspect ofthe present invention;

FIG. 29(a) is a plane view for illustrating a flat plate 121 made of acorrosion-resistant material;

FIG. 29(b) is a view for illustrating a state in which groove 122 isformed at the flat plate 121;

FIG. 29(c) is a sectional view of a nozzle portion 123 formed by joininga pair of the flat plates 121;

FIG. 29(d) is a sectional view illustrating a state in which the nozzleportion 123 is fitted to a crucible 125;

FIG. 30(a) is a plane view of a plane plate 126 made of acorrosion-resistant material formed with plural rows of groove 127;

FIG. 30(b) is a perspective view of a nozzle portion 128 formed bycombining a pair of the plane plates 126;

FIG. 30(c) is a perspective view for illustrating a state in which thenozzle portion 128 is attached to a single crystal-growing crucible 131;

FIG. 31 is a partially cut perspective view for illustrating a state inwhich a plurality of nozzle portions 134 made of tubular bodies arecontacted to adjacent ones in a line;

FIG. 32 is a graph showing the relationship between the wavelength andthe intensity of the output light beam in connection with the fourthaspect of the present invention;

FIG. 33 is a graph for illustrating how to measure the intensity ofoutput light beams having wavelengths on opposite sides of a targetwavelength λo;

FIG. 34 is a sectional view for outlining a single crystal-producingapparatus according to an embodiment of the fourth aspect of the presentinvention; and

FIG. 35 is a block diagram for illustrating a feed back control systemusing a pair of laser beam sources 147A and 147B and a pair of lightbeam-receivers 148A and 148B.

DETAILED DESCRIPTION OF THE INVENTION

Now, embodiments of the single crystal-producing apparatus according tothe first aspect of the present invention will be explained.

FIG. 1 is a block diagram of schematically illustrating the singlecrystal-producing apparatus according to the an embodiment of the firstaspect of the present invention. In the single crystal-producingapparatus, a heater 4A is provided inside an upper furnace 2, and aheater 4B is provided in a lower furnace 3. Temperature detectors(preferably thermocouples) 5A, 5B, 5C, 5D and 5E are arranged atspecific locations of the upper and lower furnace. Signal cords areextended from each temperature detector to a controller 9. A crucible 11is placed inside an inner space 10 of the upper furnace 2, and a singlecrystal body is drawn out into an inner space 18 of the lower furnace 3through a nozzle of the crucible 11. A preferred embodiment of thisportion will be explained later. A raw material feeder 1 is arrangedabove the upper furnace 2, and a feed port 1a of this raw materialfeeder 1 is opened to toward an upper face of the crucible 11. The rawmaterial feeder 1 is also connected to the controller 9 through a signalcord.

A photographing device 6 for the single crystal body 12 is arrangedunder the lower furnace 3, and connected to the monitor 7. A movingdevice 13 schematically shown in the form of a block is arranged underthe photographing device 6, and a cutter is under the moving device 13.Both the moving device 13 and the cutter 14 are connected to thecontroller. A reference numeral 16 denotes a cut portion of the singlecrystal body, and 15 denotes a single crystal product cut with aspecified shape and dimension.

A transfer device 17 is arranged under the single crystal product, andthe single crystal product 15 is moved into the transfer device 17 in adirection of the arrow A. The single crystal-producing apparatus isobserved through a terminal unit 8, and controlled by the controllerthrough the terminal unit.

In the following, preferred embodiments of various portions of thesingle crystal-producing apparatus will be explained in more detail.FIG. 2 is a sectional view for outlining a single crystal-growingdevice, and FIGS. 3(a) and 3(b) are schematic views for illustrating adistal end portion of a nozzle portion.

Inside the furnace is provided a crucible 20. An upper furnace isarranged to cover the crucible 20 and an upper space 10 around it. Aheater 4A is buried in the upper furnace 2. The nozzle portion 25extends downwardly from an lower end portion of the crucible 20, and adrawing hole 25a is formed at a lowermost end of the nozzle portion 25.A lower furnace 3 is arranged to cover the nozzle 25 and a space 28around it. A heater 4B is buried in the lower furnace. The heatingfurnace can of course be modified in various ways. For example, althoughthe heating furnace is divided into two zones, i.e., the upper and lowerfurnaces in FIG. 2, the heating furnace may be divided into three ormore zones. Both of the crucible 20 and the nozzle 25 are made of acorrosion-resistive conductive material.

One electrode extending from an electric power source 22A is connectedto a location B of the crucible 20, and the other electrode of theelectric power source 22A is connected to a corner C of a lower bentportion of the crucible 20. One electrode extending from an electricpower source 22B is connected to a location D of the nozzle portion 25,and the other electrode of the electric power source 22B is connected toa lower end of the nozzle portion 25. The electrocity-passing mechanismsmentioned above are separated from each other so that voltages appliedto these mechanisms may be independently controlled.

Further, an after-heater 66 is provided inside the space 18 such thatheater 66 surrounds the nozzle at a given interval. Inside the crucible20 is upwardly extended an intake tube 23, which has an intake hole 24at its upper end. The intake hole 24 is located at a location slightlyprotruding into a bottom portion of a melt 21 inside the crucible 20.

Alternatively, the melt intake hole 24 may be formed at the bottom ofthe crucible so that the intake hole 24 may not be located to protrudethe intake tube 20 from the bottom of the crucible 20. In this case, nointake tube 23 is provided. However, as the crucible is used for a longtime, impurities in the melt may gradually accumulate in the bottomportion of the crucible. When the intake opening 24 is provided at theupper end of the intake tube 23, the impurities at the bottom is areunlikely to enter the intake opening 24 even if impurities areaccumulated on the bottom of the crucible, because the intake tube 23protrudes in the crucible from its bottom.

The upper furnace 2, the lower furnace 3 and the after heater 66 arecaused to generate heat to properly set the temperature distributioninside each of the spaces 10 and 18, the raw material for the melt isfed into the crucible 20, and the crucible 20 and the nozzle portion 25are caused to generate heat through application of electric powerthereto. In this state, as shown in FIG. 3(a), the melt 21 slightlyprotrudes from a drawing opening 25a in a single crystal-growing section26 at a lower end portion of the the nozzle portion 25, and is heldtherein by its surface tension to form a relatively flat surface 29.

The gravity acting on the melt 21 inside the nozzle 25 is largelyreduced through contacting of the melt with the inner surface of wall ofthe nozzle 25. In particular, if the inner diameter of the nozzleportion 25 was set at not more than 0.5 mm, the above-mentioned uniformsolid phase/liquid phase interface (meniscus) could be formed.

In this state, a seed crystal 27 is moved upwardly as shown in adirection of the arrow F, so that an end face 27a of the seed crystal 27is contacted with the above surface 29 of the melt. Then, as shown inFIG. 3(b), the seed crystal 27 is downwardly pulled down. The uniformmeniscus 30 is formed between the upper end of the seed crystal 27 andthe melt 21 is drawn downwardly through the nozzle portion 25. As aresult, as shown in FIG. 2, the single crystal body 12 is continuouslyformed above the seed crystal 27, and pulled downwardly. A referencenumeral 28 denotes a mechanism for pulling down the seed crystal 27.

On the other hand, if a conventional crucible is used and an amount ofthe raw material powder fed to the crucible is increased, an expandedportion of the melt is formed downwardly swelled from a drawing hole ofthe crucible. In this state, if an end face of a seed crystal iscontacted with the melt, no good solid phase/liquid phase interface isformed.

Next, a preferred concrete configuration of the nozzle portion for theproduction of a single crystal plate will be explained. As shown in FIG.4(a), plural rows of slender grooves 32 are formed in parallel at a flatplate 31. A planar nozzle portion 35 is formed by bonding the planarplates 31 as shown in FIG. 4(b) so that plural rows of melt flowpassages 33 may be formed in the nozzle portion 35. A reference numeral34 denotes a joint.

As shown in FIG. 4(c), the nozzle portion 35 is joined to the bottom ofan elongated crucible 37. The melt in the crucible 37 flows outdownwardly through the melt flow passages 33 of the nozzle 35. At thattime, the melts flowing down through the melt flow passages 33 arecombined together along the bottom face 35a of the nozzle portion 33,and the combined melt is solidified immediately below the bottom face35a. Accordingly, the planar single crystal 36 is pulled downwardlythrough the nozzle portion 35. According to this type of the nozzleportion, the melt flow passages 33 each having a small diameter can beeasily formed in the nozzle portion for the production of the singlecrystal plate.

FIG. 5 is a schematic view for illustrating a single crystal-growingdevice with a plurality of drawing holes. A melt 21 is received in acrucible 38, and a plurality of the drawing openings 40 are provided inthe bottom of the crucible 38 so that single crystal bodies 12 may bepulled down through the respective drawing openings 40 in a direction ofthe arrows H. In order to supplement reduction in the amount of the meltin the crucible, a fresh single crystal raw material 39 is supplementedto the crucible in a direction of the arrow G.

FIG. 6 is a perspective view for illustrating a preferred embodiments ofholders and cutters, and FIG. 7 is a side view for illustrating aprincipal portion thereof. FIG. 8 is a front view for illustratingchucks of the holder and their vicinity. Feed screws 42A and 42B areprovided for a pair of respective frame members 41A and 41B, and holders44A and 44B are fixed to the respective feed screws 42A and 42B. Cuttersare provided under the respective holders 44A and 44B, and each ofcutting members 45A and 45B of the cutters are coupled to a cylinder 46via a shaft 47. Motors 43A and 43B are accommodated in a base tableunder the frame members 41A and 41B. The motors 43A, 43B are actuated torotate the feed screws 42A, 42B so that the holder and the cutter may bemoved up or down.

A concrete construction example of the holder 44A, 44B is shown in FIG.8. A shaft 49 is connected to a cylinder 48, and a chuck 53A is fixed tothe shaft 49 by a fixing member 52A. The shaft 49 is mechanicallyconnected to a shaft 50 parallel thereto by a link mechanism 51. A chuck53B is fixed to this shaft 50 by a fixing member 52B. The cylinder 48can be driven in the arrow directions indicated by I. If the cylinder 48is moved left in FIG. 8, the shaft 49 and the chuck 53A move toward theleft side, whereas the shaft 50 and the chuck 53B move toward the rightside. Consequently, the distance between the chucks 53A and 53B becomesgreater to release grasping of the single crystal body. When the singlecrystal is to be grasped, the cylinder 48 is driven toward right, andthe shaft 49 and the chuck 53A are moved toward the right side, whereasthe shaft 50 and the chuck 53B move toward the left side.

When the single crystal body is to be downwardly fed, the outerperiphery of the single crystal body is first grasped by the holder 44B,and then the feed screw is driven to move the holder 44B down to aspecific location. At that time, as shown in FIG. 7, the cylinder 46 isdriven to protrude the cutting member 45B so that the cutting member 45Bmay be brought into contact with the single crystal body 12, and causedto cut the single crystal body 12 upon pushing. Thereby, a singlecrystal product 15 is formed. Then, while the grasping of the singlecrystal body with the holder 44B is released, the single crystal body isgrasped by the holder 44A at a given location, and then the holder 44Ais in turn moved downwardly. During this step, the holder 44B is movedup to a specific upper location. In this way, the single crystal body 12is alternatively grasped by and released from the holders 44A and 44B,and successively moved downwardly and cut, so that the single crystalbody can be successively and automatically moved and cut. The aboveoperations of the holders, the feed screws, etc. are controlled by thecontroller, but the controlling itself can be made according to a knownmethod.

FIG. 9 is a side view for outlining other preferred embodiments of thesingle crystal-moving device and cutters, and FIG. 10 is a perspectiveview for illustrating a driving mechanism for a pair of rotary bodies. Arotary shaft 67B is fixed to a rotary shaft of a motor 54 via a gearchamber 55, and a pair of wheels 68 are fixed around the rotary shaft67B such that a gap 69 is provided between a pair of the wheels 68. Byso constructing, a rotary body 66B is formed. A rotary shaft 67A isprovided to be synchronized with the rotary shaft 67B via a mechanismnot shown. A pair of wheels 68 are fixed around the rotary shaft 67Asuch that a gap 69 is provided between a pair of the wheels 68. By soconstructing, a rotary body 66A is formed. The single crystal body 12 isheld in the gaps between a pair of the rotary bodies 66A and 66B, andthen pulled downwardly.

Under the moving devices is arranged a cutter 57, which includes acutting blade 58 connected to a driving unit. The cutting blade 58 iscontacted with the single crystal body 12, and is caused to shear cutthe single crystal body 12 under application of pressure. Thereby, asingle crystal product not shown is obtained. This single crystalproduct is fallen down to a receiving box 60 along a slider 73.

The single crystal body may be fused by using a heater. For example, asschematically illustrated in FIG. 11(a), a heater 189 is opposed to thesingle crystal body 12, and as shown in FIG. 11(b), the heater 189 iscaused to generate heat, and the single crystal body 12 is locallyheated and fused. Thereby, a single crystal product 27 can be obtained.At that time, a portion of the single crystal body 12 is located insidea recess 189a of the heater 189, and the heater is caused to generateheat in the state that the heater does not contact the single crystalbody 12. Alternatively, the single crystal body 12 may be fused in thestate that the heater 189 is brought into contact with the singlecrystal body 12.

Referring to FIG. 12(a), a single crystal body 12 is on a screen 61 of amonitor 7. A scale 62 is arranged vertically to the single crystal 12,which enables the outer dimension of the single crystal body 12 to bemeasured.

As illustrated in FIG. 12(b), a laser beam 64 is irradiated upon theouter periphery of a single crystal body 63, and a portion of theirradiated light beam not interrupted by the single crystal body 63 isreceived by a light beam-receiving device not shown. Thereby, aX-direction dimension of the single crystal body 63 can be measured.Simultaneously, a laser beam 65 is irradiated upon the the outerperiphery of the single crystal body 63 in a direction orthogonal tothat of the laser beam 64, and a portion of the irradiated light beamnot interrupted by the single crystal body 63 is received by a lightbeam-receiving device not shown. Thereby, a Y-direction dimension of thesingle crystal body 63 can be measured.

In the following, more concrete experimental results will be explained.

Example 1

Growing of a KLN single crystal fiber

According to the process illustrated in connection with FIG. 1, a KLNsingle crystal fiber was produced. As the single crystal-growing device,that shown in FIG. 2 was used. The temperature of the entire interior ofthe furnace was controlled by the upper furnace 2 and the lower furnace3. The growing device was so designed that the temperature gradient ofan area near the single crystal-growing section 26 might be controlledby applying electric power to the nozzle 25 and making the after-heater66 generate heat.

A powdery raw material was prepared by mixing potassium carbonate,lithium carbonate and niobium oxide in a molar composition ratio of30:20:50. Into the crucible 20 made of platinum was put about 50 g ofthe above powdery raw material, and the crucible 20 was set at aspecified location. Above the crucible 20 was set the raw materialfeeder 1, and a weight detector (not shown) was arranged in an upperportion of the crucible so that the feed speed of the raw material maybe controlled based on a signal from the weight detector. Thetemperature of the space 10 inside the upper furnace 2 was adjusted to atemperature range of 1100°-1200° C., thereby the raw material was meltedinside the crucible 20. The temperature of the space 18 inside the lowerfurnace 3 was uniformly controlled to the temperature range of500°-1000° C. While a given electric power was applied to the crucible20, the nozzle portion 25 and the after-heater 66, a single crystal bodywas grown. At that time, the single crystal body was excellently grownunder the controlled condition that the temperature of the singlecrystal-growing section was set at 1050°-1150° C., and the temperaturegradient at the single crystal-growing section was controlled to 10°-50°C/mm.

The cross sectional shape of each of the inner and outer peripheries ofthe nozzle portion 25 was circular with the outer diameter of 1 mm, theinner diameter of 0.1 mm and the length of 20 mm. The plane shape of thecrucible 20 was circular with the diameter of 30 mm and the height of 30mm.

The single crystal-moving device was used, which included the rotarybodies as shown in FIGS. 9 and 10, and the cutter shown in FIGS. 11(a)and 11(b) were used with the heater made of a platinum wire. This movingdevice enabled the single crystal fiber to be drawn down at a verticallyuniform speed in a range of 2-200 mm/hr. As an observing device, the CCDimage-photographer and the monitor shown in FIGS. 1 and 12(a) were used.

In order to first effect seeding, a seed crystal was moved up from alower side, and contacted to the melt. After a good meniscus was formedat the interface between the seed crystal and the melt, the seed crystalwas drawn down at a speed of 20 mm/hr, and a single crystal fiber wasgrown. By so doing, the single crystal fiber or single crystal bodyhaving a sectional shape of 1×1 mm was grown. When the length of thegrown single crystal body reached about 200 mm, the single crystal fiberwas grasped between a pair of the rotary bodies. Then, the seed crystalportion was cut off by applying electric power to the heater 169. Thesingle crystal fiber exists between the holder and the nozzle portion ofthe single crystal-growing device.

As the single crystal fiber grew, the melt inside the crucible decreasedand the weight of the entire crucible, that is, the weight of the meltdecreased. Therefore, the total weight of the crucible and the melt wasmeasured by a load cell, and a fresh raw material was fed so that themeasured result might be almost constant with an error of within ±10 mg.Since the single crystal fiber grew 60 mm in about 3 hours, electricpower was applied to the heater every three hours to cut the singlecrystal fiber. Thereby, single crystal fiber products having a dimensionof 1×1×60 mm were continuously produced. In this state, the aboveoperation was continued for one week to obtain 56 single crystal fiberproducts.

With respect to the thus obtained single crystal fiber products, thesecond harmonic wave-generating characteristic was measured. As aresult, it was found out that a phase matched wavelength was almostconstant within a detection variation of ±0.2 μm with respect to atarget one of 840 nm. Further, an output conversion efficiency obtainedwas almost the same as its theoretical value, and its variation iswithin ±1%, which is the detection limit of this measurement.

Example 2

Multiple growing of Nd-LN single crystal fibers

Nd-LN single crystal fibers were grown according to the processexplained by referring to FIG. 1. The same growing crucible shown inFIG. 5 except that the number of the nozzles were 10 was used. Thefurnace for the single crystal-growing device as shown in FIG. 2 wasused. The temperature of the entire interior of the furnace wascontrolled by the upper furnace 2 and the lower furnace 3. Thetemperature gradient near the single crystal-growing section 26 wascontrolled by feeding the electric power to the nozzle portion 25 andmaking the after heater 66 generate heat.

A powdery raw material was prepared by mixing neodymium oxide, lithiumcarbonate and niobium oxide at a molar composition ratio of 1:49:50.Into the platinum crucible 38 was put 100 g of this powdery rawmaterial. Above the crucible 38 was set the raw material feeder 1. Athermocouple was arranged near the surface of the melt inside thecrucible, and the feeding of the raw material into the melt inside thecrucible was controlled based on a signal from the thermocouple.

The temperature of the space 10 inside the upper furnace 2 was adjustedto a temperature range of 1200°-1300° C., thereby melting the rawmaterial inside the crucible 38. The temperature of the space 18 insidethe lower furnace 3 was uniformly controlled to the temperature range of600°-1200° C. While a given electric power was applied to the crucible38, the nozzle portion 40 and the after-heater 66, a single crystal bodywas grown. At that time, the single crystal body was excellently grownunder the controlled condition that the temperature of the singlecrystal-growing section was set at 1200°-1300° C., and the temperaturegradient at the single crystal-growing section was controlled to 10°-50°C./mm.

The single crystal-moving device was used, which included the holdersand the cutters as shown in FIGS. 6, 7 and 8. In this experiment, eachset of the holder and the cutter was arranged at a locationcorresponding to each nozzle portion. This moving device enabled thesingle crystal fiber to be pulled down at a vertically uniform speed ina range of 2-200 mm/hr. As an observing device, the CCDimage-photographer and the monitor shown in FIGS. 1 and 12(a) were used.

A seed crystal was grasped by a first uppermost holder. In order tofirst effect seeding, a seed crystal was moved up from a lower side, andcontacted to the melt. After a good meniscus was formed at the interfacebetween the seed crystal and the melt, the seed crystal was pulled downat a speed of 25 mm/hr, and a single crystal fiber having a sectionalshape of 0.6×0.6 mm was grown. When the length of the thus grown singlecrystal body reached about 200 mm and the first holder was located 75 mmlower than the second one, the single crystal fiber was grasped by thesecond holder, and the single crystal fiber was pulled down by a speedof 25 mm/hr. Thereafter, the grasping of the single crystal fiber withthe first holder was released, and the first holder was moved upwardly.The single crystal fiber was cut by the cutting member under the secondholder, and the single crystal fiber product was moved to a singlecrystal fiber-stocking section. Such single crystal fiber products couldbe continuously produced by repeating the above process.

As the single crystal fiber grew, the melt inside the crucibledecreased. Thus, the temperature was measured by the thermocouplearranged at a location slightly higher than the surface of the meltinside crucible, and changes of the melt surface were detected based onchanges of the thus measured temperature. A temperature signal was sentto the controller, which feed back controlled the feeding of the rawmaterial so that variations in the height of the melt surface might bewithin ±0.1 mm from a target one. Since the single crystal fiber grew 75mm in about 3 hours, electric power was applied to the heater everythree hours to cut the single crystal fiber. Thereby, single crystalfiber products having a dimension of 0.6×0.6×75 mm were continuouslyproduced. In this state, the above operation was continued for one weekto obtain 56 single crystal fiber products.

With respect to all the thus obtained Nd-LN single crystal fiberproducts, the laser oscillating characteristic was measured. As aresult, it was confirmed that almost same output conversion efficiencyat 1060 nm was obtained, and detection variations were within ±1%. Theelementary analysis of the composition distribution with EPMA revealedthat with respect to the charged composition of 1.0 mol %, a variationin each component of the composition was controlled to within ±2%variation from the first molar ratio, which is the detection limit ofthis measurement.

Example 3

Growing of a KLN single crystal plate

According to the process illustrated by referring to FIG. 1, a KLNsingle crystal plate was produced. As the single crystal-growingcrucible, that shown in FIGS. 4(a) to 4(c) was used. The furnace for thesingle crystal-growing device as shown in FIG. 2 was used. Thetemperature of the entire interior of the furnace was controlled by theupper furnace 2 and the lower furnace 3. The growing device was designedsuch that the temperature gradient of an area near the singlecrystal-growing section 26 might be controlled by applying electricpower to the nozzle 25 and making the after-heater 66 generate heat.

As the flat plate 31 was used a platinum plate having a dimension of 30mm×30 mm×0.6 mm. Grooves 32 were formed at this platinum plate bymechanical cutting using a dicing machine. The interval between theadjacent grooves 32 was 5 mm, and the width of each groove was 0.1 mm. Aplanar nozzle portion 35 having a thickness of 1.2 mm was formed byjoining two platinum plates 31. As explained in connection with FIGS.4(a) to 4(c), the melt was flown through the melt flow passages 33.

A powdery raw material was prepared by mixing potassium carbonate,lithium carbonate and niobium oxide in a molar composition ratiomentioned later. Into the crucible 37 made of platinum was charged 500 gof the above powdery raw material. Above the crucible 20 was set the rawmaterial feeder 1. The thermocouple was set near the surface of the meltinside crucible, and the feeding of the raw material to the melt wascontrolled based on a signal from the thermocouple.

The temperature of the space 10 inside the upper furnace 2 was adjustedto a temperature range of 1100°-1200° C., thereby the raw material wasmelted inside the crucible 37. The temperature of the space 18 insidethe lower furnace 3 was uniformly controlled to the temperature range of500°-1000° C. While given electric power was applied to the crucible 37,the nozzle portion 25 and the after-heater 66, a single crystal body wasgrown. At that time, the single crystal body was excellently grown underthe controlled condition that the temperature of the singlecrystal-growing section was set at 1050°-1150° C., and the temperaturegradient at the single crystal-growing section was 10°-50° C./mm.

The single crystal plate-moving device was used, which included therotary bodies as shown in FIGS. 9 and 10. A cutter was used, which cutthe single crystal plate by irradiating carbon dioxide laser beam uponit. This moving device enabled the single crystal plate to be pulleddown at a vertically uniform speed in a range of 2-200 mm/hr. Themeasuring device shown in FIG. 12(b) was used, which observed thedimension of the single crystal plate by using the laser beams. Underthe cutter was arranged a transfer device for transferring cut singlecrystal plate products by a belt conveyor in the state that the cutsingle crystal plate products were placed on a holding member andtransferred.

In addition, an observing device for the composition of the singlecrystal plate was installed, which includes a titanium-sapphire laserbeam source and spectrum analyzer for analyzing output light beam fromthe single crystal plate.

In order to first effect seeding, a seed crystal was moved up from alower side, and contacted to the melt. After a good meniscus was formedat the interface between the seed crystal and the melt, the seed crystalwas pulled down at a speed of 18 mm/hr, and a single crystal plate wasgrown. When the length of the thus grown single crystal body reachedabout 200 mm with a sectional shape of 50 mm×1 mm, the single crystalplate was grasped between a pair of the rotary bodies. Then, the seedcrystal portion was cut off by irradiating the carbon dioxide laser, andthe moving device was moved down to the lowermost portion.

As the single crystal plate grew, the melt inside the crucibledecreased. Thus, the temperature was measured by the thermocouplearranged at a location slightly higher than the surface of the meltinside crucible, and changes of the melt surface were detected based onchanges of the thus measured temperature. A temperature signal was sentto the controller, which feed back controlled the feeding of the rawmaterial so that variations in the height of the melt surface might bewithin ±0.1 mm from a target one.

A laser beam of near a target phase matched wavelength (840 mn) wasirradiated upon the single crystal plate from the titanium-sapphirelaser beam source, and an output light was analyzed by the spectrumanalyzer. As raw materials, powders having the following two kinds ofcompositions were used.

Powder 1: K₃.1 Li₂ Nb₅ O

Powder 2: K₂.9 Li₂ Nb₅ O

First, Powders 1 and 2 were mixed at a ratio of 1:1, which was put intothe crucible. When the peak wavelength shifted to a longer side, theamount of Powder 1 was increased, whereas when the peak wavelengthshifted to a shorter side, the amount of Powder 2 was increased. By sodoing, the composition of the single crystal plate was controlled.

As a result, the phase matched wavelength of the single crystal platewas controlled to an accuracy of not more than 0.2 nm. That is, thecomposition of the KLN single crystal could be controlled to a highaccuracy of not more than 0.01 mol % than ever before.

Since the single crystal fiber grew 50 mm in about 3 hours, the singlecrystal plate was cut by irradiating the carbon dioxide laser beamthereupon every three hours to cut the single crystal plate. Thereby,single crystal plate products having a dimension of 50 mm×50 mm×1 mmwere continuously produced. In this state, the above operation wascontinued for one week to obtain 56 single crystal plate products.

With respect to all of the thus obtained single crystal products, theproperty of the second harmonic generation plate was measured. As aresult, it was confirmed that a phase matched wavelength was almostconstant within a detection variation of ±0.2 nm with respect to atarget one of 840 nm. Further, an output conversion efficiency obtainedwas almost the same as its theoretical value within ±1% variation, whichis the detection limit of this measurement.

Next, embodiments of the second aspect of the present invention will beexplained.

FIG. 13 is a schematic cross-sectional view of the producing apparatusfor growing a single crystal, and the state of the distal end portion ofthe nozzle portion thereof will be explained using FIGS. 3(a) and 3(b).

A crucible 20 is disposed in the interior of the furnace body. An upperfurnace 2 is arranged to surround the crucible 20 and its upper space10. The upper furnace 2 has a heater 4A embedded therein. A nozzleportion 25 extends downwardly from the lower end of the crucible 20 andhas an opening 25a at the lower end. A lower furnace 3 is arranged tosurround the nozzle portion 25 and its surrounding space 18. The lowerfurnace 3 has a heater 4B embedded therein. The crucible 20 and thenozzle portion 25 are respectively made of a corrosion-resistantelectrically conductive material. The heating furnace can of course bemodified variously. For example, though the heating furnace is dividedinto two heating zones in FIG. 13, the heating furnace may be dividedinto at least three heating zones.

An electrode of an electric power source 22A is connected to a portion Bof the crucible 20 through a leading wire 68 and the other electrode ofthe power source 22A is connected to a portion C of the crucible 20. Anelectrode of an electric power source 22B is connected to the portion Dthe nozzle portion 25 and the other electrode of the power source 22B isconnected to the lower end E of the nozzle portion 25. These electricpower supplying mechanisms are separated from each other and constructedto control its voltage independently.

In addition, an after-heater 66 is arranged in the space 18 to surroundthe nozzle portion 25 with a spacing. An intake tube 23 extends upwardlyand has an intake hole 24 at the upper end. The intake tube 23 is alittle protruded upwardly from the bottom of the melt 21.

If the temperature gradient of the nozzle portion 15 has been optimizedby the furnace body (a heat-generating member and a refractivematerial), the after-heater 66 is not indispensable and may be omitted.

The intake hole for the melt may be provided at the bottom of thecrucible such that it does not protrude from the bottom of the crucible.In such a case, the intake tube 23 is not provided. However, when thecrucible is used for a prolonged period of time, impurities in the meltare occasionally gradually accumulated on the bottom of the crucible. Bythe provision of the intake hole 24 at the upper end of the intake tube23 as in this embodiment, the impurities on the bottom of the crucibleare hardly introduced in the intake hole 24 even if the impurities areaccumulated on the bottom of the crucible, because the intake tube 23 isprotruded from the bottom of the crucible.

The upper furnace 2, the lower furnace 3 and the after-heater 66 areheat generated to suitably determine the temperature distributions inthe spaces 10, 18, the raw material for forming the melt is fed in thecrucible 20, and the crucible 20 and the nozzle portion 25 areheat-generated by supplying an electric power thereto. At this state, atthe single crystal-growing section 26 existing at the lower end of thenozzle portion 25, the melt 21 is slightly protruded from the opening25a and retained thereat by the surface tension to form a relativelyflat surface 29.

The gravity acting on the melt 21 in the nozzle portion 25 is largelydecreased by the contact of the melt with the inner wall surface of thenozzle portion 25. Particularly, by using the nozzle portion 25 of aninner diameter of not more than 0.5 mm, a uniform meniscus could beformed as described above.

At this state, the seed crystal 27 is moved upwardly as shown by thearrow F to contact its upper end surface 27a with the lower surface 29of the melt 21. Then, the seed crystal 27 is pulled downwardly as shownin FIG. 3 (b). At that time, a uniform meniscus is formed between theupper end surface of the seed crystal 27 and the lower end surface ofthe melt 21 drawn downwardly from the nozzle portion 25.

As a result, a single crystal fiber 12 is continuously formed on theseed crystal 27 and pulled downwardly. In this embodiment, the seedcrystal 27 and the single crystal fiber 12 are drawn by a pair ofrollers 67.

Meanwhile, in case if a conventional crucible is used and the amount ofthe material powder initially charged in the conventional crucible isincreased, a round expanded surface of the melt is formed downwardlyfrom the opening 25a of the nozzle portion 25. If the upper end surfaceof the melt is contacted to the upper end surface of the seed crystal27, a good meniscus is not formed.

The producing apparatus shown in FIG. 14 is substantially the same asthat shown in FIG. 13, so that the same functional members are allottedwith the same reference numerals as in FIG. 13 and the explanations ofFIG. 13 are referenced in FIG. 14. However, the producing apparatusshown in FIG. 14 is not provided with the mechanism of supplyingelectric power to the crucible 20 per se as used in the producingapparatus of FIG. 13, so that the crucible 20 per se is notheat-generated. However, in this case also, the raw material powder inthe crucible 20 can satisfactorily be heated by adjusting thetemperature of the upper furnace 2, or if necessary by providing andusing a not shown radio frequency heat-generating mechanism around thecrucible 20.

FIG. 15 is a schematic cross-sectional view of another embodiment of thepresent producing apparatus. The same functional members as in FIGS. 13and 14 are allotted with the same reference numerals and explanationsthereof are omitted. Also, the neighboring portions, such as, the upperand lower furnaces shown in FIGS. 13 and 14 are omitted in FIG. 15. Inthe producing apparatus shown in FIG. 15, electrodes of the electricpower source 22A are connected to the upper end F and the substantiallycentral portion G of the crucible 20, electrodes of the electric powersource 22B are connected to the substantially central portion G and thelower end H of the crucible 20, and electrodes of an alternating currentelectric power source 22C are connected to the lower end H of thecrucible 20 and the upper end I of the nozzle portion 25. The nozzleportion 25 is connected to an alternating current power source 22through leading wires. These electric power supplying mechanisms areseparated from each other and constructed to control its voltageindependently.

FIG. 16 is a schematic cross-sectional view of still another embodimentof the producing apparatus showing a shape of the crucible. A nozzleportion 169 extends downwardly from the lower end of the crucible 20 andhas an opening 169a at the lower end. The single crystal fiber or plate12 is pulled down from the opening 69a. The intake tube 23 extendsupwardly in the crucible 20 and has the intake hole 24 at the upper end.

The crucible 20, the intake tube 23 and the nozzle portion 169 arerespectively made of a corrosion-resistant electrically conductivematerial. Electrodes of the electric power source 22A are connected tothe upper end B and the lower end C of the crucible 20. A circularshaped heat-generating member 170 is arranged around the nozzle portion169. An electrode of the electric power source 22 is connected to theupper end D of the heat-generating member 170 through a leading wire 178and the other electrode of the electric power source 22 is connected tothe lower end E of the heat-generating member 170. These electric powersupplying mechanisms are separated from each other and constructed tocontrol its voltage independently.

In order to heat the nozzle portion, a not shown radio frequencyheat-generating mechanism may be provided around the nozzle portion, andthe single crystal could be grown by precisely controlling themechanism.

If a direct current power source is connected to the nozzle portion 169,bubbles of gas are occasionally formed by electrolysis of the ionizedmelt. In such a case, an alternating current power source has to beconnected to the nozzle portion 169. However, if the circularheat-generating member 170 is arranged around the nozzle portion 169 asin this embodiment, a direct current power source may be connected tothe heat-generating member 170.

FIG. 17 is a schematic cross-sectional view of still another embodimentof the producing apparatus showing a shape of the crucible 150 usedtherein. A nozzle portion 25 extends downwardly from the lower end of amain body 77 of a crucible 150, while an intake tube 23A extendsupwardly from the bottom of the crucible 150. In the main body 77 of thecrucible 150, a partition wall 71 which is circular viewed in plan viewis disposed between the inner wall of the main body 77 and the intaketube 23A to form a space 73 between the inner wall of the main body 77and the partition wall 71 as well as a space 76 between the partitionwall 71 and the intake tube 23A. The partition wall 71 may be fixed tothe inner wall of the main body 77 at a portion not shown or may befixed to an exterior member of the crucible 150.

The lower end of the partition wall 71 is not contacted to the bottom 75of the main body 77, so that a gap 74 exists between the partition wall71 and the main body 77. Therefore, if the raw material powder ischarged in the space 73 from a raw material supply hole 72 existing atthe outside of the partition wall 71, the raw material powder is meltedin the space 73 and passed from the space 73 to the space 76 through thegap 74 and rises in the space 76 and introduced in the intake tube 23Afrom the intake hole 24.

Processing of a noble metal, such as, platinum to form the nozzleportion of a fine inner diameter of not more than 0.2 mm is usuallydifficult and much expensive. Therefore, the inventors have found outthat such a small nozzle portion of a fine inner diameter of not morethan 0.2 mm can be produced by the following method.

That is, the inventors produced such nozzle portion by forming a groovein a corrosion-resistant member made of a corrosion-resistant metal or acorrosion-resistant ceramics preferably of a plate shape, and adheringor joining the grooved member to the other corrosion-resistant memberpreferably of a plate shape. In such a nozzle portion, the groove servesas an elongated passage of a fine diameter for the melt.

At that time, the passage for the melt may be prepared by forming thegroove in both the flat plates and integrally uniting the grooves whenadhering the flat plates. Alternatively, the passage may be prepared byforming the groove in one flat plate, while leaving the other flat plateas it is, and adhering the two flat plates to obtain the passage formedby the groove in the flat plate.

In addition, the inventors could produce a single crystal plate asdescribed later in detail by forming a plurality of grooves in thenozzle portion to form the passages for the melt and drawing the meltsimultaneously from the passages.

In these cases, preferably the grooves have respectively a width of0.01-0.5 mm, and a spacing of 0.1-10 mm. The grooves may have a squareshape, a rectangular shape, V-shape or a half circular shape.

Concretely explaining, an elongated flat plate 78 is prepared as shownin FIG. 18 (a), and an elongated groove 79 is formed longitudinally inthe flat plate 78 as shown in FIG. 18 (b). The same work is effectedusing another flat plate 78. Two sheets of such flat plates 78 areadhered facing the grooves 79 to each other to prepare a nozzle portion80 as well as a passage 81 in the nozzle portion 80 as shown in FIG. 18(c). The nozzle portion 80 is joined to the bottom 82a of a crucible 82and the melt is flowed down in the passages 81 as shown in FIG. 18 (d).If such a means is used, a nozzle portion having a fine inner diameterof not more than 0.2 mm for forming the single crystal fiber can easilybe prepared. Of course, the nozzle portion may have an inner diameter ofnot less than 0.2 mm.

Next, concrete shapes of the nozzle portion for producing the singlecrystal plate will be explained. The inventors have found out that inthe μ pulling down process the single crystal plate can be pulled downby preparing a flat surface of a plate shape corresponding to thecross-section of the single crystal plate, forming a plurality ofelongated passages for the melt, drawing the melt simultaneously fromthe passages downwardly, and flowing and uniting the drawn melt alongthe flat surface.

In this embodiment, the whole of the nozzle portion can be made to aplate shape. Also, the nozzle portion may have a tubular shape and adiameter expanded portion at the distal end and the distal end surfaceof the diameter expanded portion may have a flat surface as describedabove. The nozzle portion may be made of a plurality of tubular membersand the tubular members may be integrally joined to each other to forman integral flat surface composed of the distal end surfaces of thetubular members.

For example, a plurality of rows of elongated parallel grooves 32 areformed in a flat plate 31 as shown in FIG. 4 (a). The same work iseffected using another flat plate 31. Two sheets of such flat plates 31are adhered to prepare a flat plate shaped nozzle portion 35 as well aspassages 33 in the nozzle portion 35 as shown in FIG. 4 (b). Thereference numeral 34 denotes a joint.

The nozzle portion 35 is joined to the bottom of a rectangular crucible37 as shown in FIG. 4 (c). The melt in the crucible 37 flows down in therespective passage 33 of the nozzle portion 35 to flow out from thelower end of the respective passage 33. At that time, the melt flowedout from the lower end of the respective passage 33 becomes integral andflowed on a flat bottom plate 35a of the nozzle portion 35 and assumes asolid phase at immediate below the flat bottom plate 35a to allow thepulling of a plate shaped single crystal 36 downwardly from the nozzleportion 35. In this way, the small nozzle portion 35 of a fine innerdiameter for forming the single crystal plate can easily be prepared.

In the embodiment shown in FIG. 19, a nozzle portion 83 were made of aplurality of tubular members 85. The tubular members 85 were arranged ina row such that their outer circumferential surfaces continue from eachother. Though the crucible portion was omitted in FIG. 19, a crucible,such as, the crucible 37 as shown in FIG. 4 (c) may be used. The tubularmembers 85 have therein respectively a passage 84 for the melt and hasan opening at the lower end bottom surface 85a thereof.

The melt in the crucible flows down in the respective passage 84 of therespective tubular members 85 and flowed out therefrom to the lower endbottom surface 85a. At that time, the melt flowed out from therespective passage 84 is made integral and flowed on the a flat endsurface 87 composed of the bottom surfaces of the tubular members 85 toassume a solid phase at immediate below the flat end surface 87 therebyto allow the downward pulling of a plate shaped single crystal 86 fromthe nozzle portion 83.

Also, the nozzle portion may have a diameter expanded portion at thedistal end. Namely, if the nozzle portion is formed from a high meltingpoint metal, such as, platinum, preferably the nozzle portion has athickness of not more than 0.2 mm in order to heat-generate the nozzleportion by passing an electric power thereto. Also, the diameter of thepassage in the nozzle portion has an upper limit, so that the outerdiameter of the nozzle portion has a limit. Meanwhile, the diameter ofthe single crystal fiber drawn from the nozzle portion is usually notmore than the outer diameter of the nozzle portion. As a result, theouter diameter of the nozzle portion is occasionally less than the outerdiameter of the desired single crystal fiber, and in such a case thesingle crystal fiber can not be drawn. As a means for solving such aproblem, the nozzle portion may be formed from the main body of arelatively small outer diameter and the diameter expanded portion of arelatively large outer diameter arranged at the distal end of the mainbody.

FIG. 20 is a schematic cross-sectional view of an embodiment of theproducing apparatus of the second aspect of the present invention. Anozzle portion 89 extends downwardly from the lower end of the crucible20. The nozzle portion 89 is formed from a main body 90 of the nozzleportion 89 and a diameter expanded portion 91 arranged at the lower endof the main body 90. The diameter expanded portion 91 has the singlecrystal growing section 26 arranged therein and an opening 91a fromwhich the single crystal fiber 12 is pulled down as shown by the arrowJ. The crucible 20, the intake tube 23, the main body 90 and thediameter expanded portion 91 of the nozzle portion 89 are respectivelymade of a corrosion-resistant electrically conductive material. Theelectrodes of the electric power source 22A are connected to theportions B and C of the crucible 20 and the electrodes of the electricpower source 22 are connected to the main body 90 of the nozzle portion89 at, for example, portions D and E through the leading wires 68.

Next, the embodiment of providing the diameter expanded portion at thedistal end of the tubular nozzle portion, the distal end having the flatsurface as described above, and pulling down the single crystal platealong the flat surface, will be illustrated. FIG. 21 is a schematiccross-sectional view of the embodiment of the producing apparatus. Thenozzle portion extends downwardly from the lower end of the crucible 20.A main body 93 of the nozzle portion has a passage 93a formed thereinand an opening 93b at the lower end of the passage 93a.

A diameter expanded portion 94 is joined below the main body 93. Thediameter expanded portion 94 has a substantially flat shaped outer shell94a and a passage 94c which extends in the vertical direction in thedrawing formed in the flat shaped outer shell 94a. A multiple number ofhorizontal passages 94b are also formed in the outer shell 94a. Thepassages 94b are regularly formed in parallel to each other with adesired spacing and have respectively an opening 94d at the distal lowerend. The diameter expanded portion 94 has a flat surface 95 formed atthe lower side.

The melt in the crucible 20 flows down in the passage 93a of the mainbody 93 of the nozzle portion, flows horizontally in the passage 94c andvertically in the respective passages 94b, and flows out from therespective opening 94d. The melt flowed out from the respective opening94d becomes integral and flowed on the flat surface 95 and assumes asolid phase at immediate below a flat surface 95 thereby to allow thepulling of a plate shaped single crystal 96 downwardly from the nozzleportion.

FIG. 22 is a schematic cross-sectional view of another embodiment of theproducing apparatus of the present invention for growing the singlecrystal. FIG. 23 is a schematic plan view of the apparatus of FIG. 22. Acrucible 101 of a substantially cylindrical shape is disposed in themelting furnace 99, and heating devices 109A, 109B and 109C are arrangedto surround the crucible 101 from, for example, three directions. Thecrucible 101 contains a melt 21. An electrode of the electric powersource 22A is connected to a portion B of the crucible 101 through aleading wire, and the other electrode of the electric power source 22Ais connected to the lower end C of the crucible 101. Though the shape ofthe bottom wall 101b is of a plate shaped in this embodiment, the shapemay be changed variously as the case maybe.

The melting furnace 99 accommodating the crucible 101 is partitionedfrom the growing furnace by a heat insulating wall 98. A nozzle portion104 is arranged at a side wall 101a of the crucible 101. The crucible101 and the nozzle portion 104 are respectively made of acorrosion-resistant electrically conductive material. The nozzle portion104 has a horizontal portion 104a protruded from the side wall 101a, avertical portion 104b extending upwardly in the vertical direction, aninserting portion 104c inserted in a through-hole 98a of the heatinsulating wall 98, and a distal end portion 104d extending downwardlyfrom the distal end of the inserting portion 104c. That is, the nozzleportion 104 has the vertical portion 104b extending upwardly viewed froma connecting portion 103 connecting the nozzle portion 104 and thecrucible 101. The nozzle portion 104 is connected to the electric powersource 22 at desired portions, for example, L and M, so as toheat-generate the nozzle portion 104.

Here, preferably the nozzle portion 104 is protruded from the crucible101 between the surface level 21a of the melt and the bottom surface 102of the crucible 101 at a height not higher than the middle point of thetwo levels. This is because, particularly when the raw material powderis supplied continuously or intermittently in the crucible, minutevariations in the composition are likely occur to adversely influenceover the composition of the oxide series single crystal, whereas theadverse influence of the continuous or spasmodic supply of the rawmaterial powder over the composition of the oxide series single crystalcan be prevented by protruding the nozzle portion 104 at a height nothigher than the middle point of the surface level 21a and the bottomsurface 102 of the crucible 101.

Beating devices 109A, 109B and 109C are heat-generated and the crucible101 is heat-generated by passing an electric current therethrough tomelt the raw material in the crucible 101. Temperature distributions inthe nozzle portion 104 is suitably determined by passing an electriccurrent therethrough so that the raw material powder is not excessivelystayed in nozzle portion 104. Simultaneously, the thickness and thematerial of the heat insulating wall 98, the temperatures of the heatingdevices and the temperature of the after-heater 107 are suitablydetermined to optimize particularly the temperature distributions in thevicinity of the single crystal growing section 26 thereby to pull downthe single crystal fiber or plate from the opening 26 of the nozzleportion. In this embodiment, the seed crystal 27 and the single crystalfiber 12, etc., are transported by the rollers 67.

In the single crystal producing apparatus shown in FIGS. 22 and 23 also,a flat surface may be formed at at least the lower distal end of thenozzle portion as described above, and the single crystal plate may bepulled downwardly along the flat surface. In this case also, a plateshaped nozzle portion may be used as described above. However, in thisembodiment, the nozzle portion itself is bent so that the drawing holeof the nozzle portion may exist at a higher position than the bottomsurface of the crucible. At that time, the plate shaped nozzle portionmay be bent, e.g., as shown in FIGS. 22 and 23 in the productionthereof.

The main body per se of the nozzle portion may have a shape of, e.g.,tubular shape as shown in FIG. 22, and the diameter expanded portion maybe formed at the above described flat surface of the distal end of thetubular nozzle portion, and the single crystal plate may be pulled downalong the flat surface. This embodiment will be illustrated withreference to FIG. 24.

FIG. 24 is a schematic partial cross-sectional view of the vicinity ofthe distal end portion of another nozzle portion viewed from the growingfurnace in the single crystal producing apparatus shown in FIGS. 22 and23. The crucible and the melting furnace, etc., of the producingapparatus in this embodiment are the same as those described in FIGS. 22and 23. A main body 110 is formed vertically downwardly at the outsideof a through-hole 98a and has the diameter expanded portion 94 joinedthereto. The main body 110 has a passage 110a formed therein and anopening 110b formed at the lower end.

The shape of the diameter expanded portion 94 is the same as that shownin FIG. 21. The melt in the crucible 20 flows down in the passage 110aof the main body 110, horizontally in the passage 94c and verticallythrough the vertical passages 94b and out from the opening 94d. The meltflowed out from the respective opening 94d becomes integral and flows onthe flat surface 95 and assumes a solid phase at immediate below the fatsurface 95 thereby to allow the pulling of the plate shaped singlecrystal 96 downwardly from the nozzle portion.

Hereinafter, the second aspect of the present invention will beexplained with reference to concrete experimental results.

Example 4

Using the single crystal producing apparatus shown in FIG. 13, a KLNsingle crystal fiber was produced according to the present inventionexcept that the nozzle portion 89 shown in FIG. 20 was used as thenozzle portion. The temperatures in the whole furnace were controlled bymeans of the upper furnace 2 and the lower furnace 3. The temperaturegradient in the vicinity of the single crystal-growing section 26 wascontrolled by the supply of electric power to the nozzle portion 89 andheat-generation of the after-heater 66. For pulling down the singlecrystal fiber, a mechanism was used which pulls the single crystal fiberdownwardly at a controlled uniform pulling rate in a range of 2-100mm/hr in the vertical direction.

Potassium carbonate, lithium carbonate and niobium oxide were reciped ina mol ratio of 30:20:50 to prepare a raw material powder. Around 50 g ofthe material powder were charged in a melting crucible 20 made ofplatinum and the melting crucible 20 was set at a desired position inthe furnace. The temperature in the space 10 of the upper furnace 2 wasadjusted to a temperature of 1,100°-1,200° C. to melt the raw materialin the crucible 20. The temperature in the space 18 of the lower furnace3 was uniformly controlled to a temperature of 500°-1,000° C. A desiredelectric power was supplied to the melting crucible 20, the nozzleportion 89 and the after-heater 66 to perform the growing of the singlecrystal. At that time, the single crystal-growing section could becontrolled to a temperature of 1,050°-1,150° C. and a temperaturegradient of 10°-150° C./mm.

The nozzle portion 89 had outer and inner cross-sections of circularshapes. In particular, the main body 90 had an outer diameter of 0.4 mm,an inner diameter of 0.2 mm and a length of 20 mm. The diameter expandedportion 91 had an outer diameter of 1.0 mm, an inner diameter of 0.2 mmand a length of 2 mm. The melting crucible 20 had a circular shape inplan view and a diameter of 30 mm and a height of 30 mm. At this state,the single crystal fiber was pulled downwardly at a pulling rate of 20mm/hr in the a axial direction to find out that a good KLN singlecrystal fiber could be pulled down. In the same manner, the singlecrystal fiber could be pulled down in the c axial direction.

The thus grown single crystal fiber having a longitudinal and lateralsize of 1 mm×1 mm and a length of 100 mm was examined with respect tothe composition distribution of the single crystal fiber viewed in thelength direction (grown direction). Concretely explaining, the singlecrystal fiber was irradiated at various portions in the longitudinaldirection by a light beam. And the wavelength of the light beam emittedtherefrom was measured to detect an SHG phase matched wavelength. Ifthere is even a slight variation in the composition of the KLN singlecrystal fiber, the SHG phase matched wavelength of the emitted lightbeam is varied by the variation in the composition.

The result of the measurement showed that the wavelength was controlledwithin not more than 1 nm. So, the composition of the single crystalfiber could be controlled with a high precision of not more than 0.01mol % of composition when, which is a high precision never attainedbefore as a KLN single crystal. The wavelength conversion efficiency ofthe KLN single crystal fiber was substantially the same with thetheoretical value with an error of not more than ±2% which is within therange of measuremental error.

Example 5

In the same manner as in Example 4, a KLN single crystal fiber was grownexcept that a raw material feeding mechanism was used in the furnace,which intermittently feeds the raw material in the melting crucible 20.Also, a cutting mechanism was arranged below the furnace, whichintermittently cuts the single crystal fiber to a desired length tocontinuously grow the single crystal fiber. With the progress of thegrowing of the single crystal fiber, the raw material powder was fed inthe melting crucible in an amount corresponding to the amounts of thecomponents drawn and evaporated from the melting crucible. In this way,a single crystal fiber of a length of around 10 m was continuouslyformed and the variation in the composition thereof was measured in thesame manner as in Example 4. As a result, the variation in thecomposition of the single crystal fiber could be controlled within notmore than 0.01 mol % over the entire length of around 10 m.

Example 6

The nozzle portion 35 and the crucible 37 as shown in FIG. 4 were usedto succeed in pulling down a KLN single crystal plate of a thickness of1 mm and a width of 30 mm. However, a platinum plate of a size of 30mm×30 mm×0.6 mm was used as the plate 31. Grooves 32 each having a widthof 0.1 mm were formed with a spacing of 5 mm in the platinum plate 31 bymechanical cutting using a dicing machine. A plate shaped nozzle portionof a thickness of 1.2 mm was prepared by joining two sheets of theplatinum plate. The melt was flowed out from the respective passage ofthe melt as explained above with reference to FIGS. 4(a)-4(c). The SHGphase matched wavelength and the wavelength conversion efficiency in thesingle crystal plate were measured to obtain the same values as those ofthe above described single crystal fiber.

Example 7

The present invention was applied to a method of growing a singlecrystal of neodymium substituted LiNbO₃. However, the amount ofneodymium substituted in this system was around 0.3 mol %, if a method,for example, a CZ method was used.

Neodymium oxide, lithium carbonate and niobium oxide were reciped in amol ratio of 1:49:50 to prepare a raw material powder. The sameapparatus as in Example 4 for producing the single crystal fiber wasused. Around 50 g of the material powder were fed in the meltingcrucible 20 and the melting crucible 20 was set at a desired position inthe furnace. The temperature in the space 10 of the upper furnace 2 wasadjusted to a temperature of 1,250°-1,350° C. to melt the raw materialin the melting crucible 20. The temperature in the space 18 of the lowerfurnace 3 was uniformly controlled to a temperature of 500°-1,200° C. Adesired electric power was fed to the crucible 20, the nozzle portion 89and the after-heater 66 to grow the single crystal.

At that time, the single crystal growing section was controlled to atemperature of 1,200°-1,300° C. and to a temperature gradient of10°-150° C./mm. At this state, the single crystal fiber was pulleddownwardly at a pulling rate of 20 mm/hr to find out that a goodNd--LiNbO₃ single crystal fiber can be drawn down.

The thus grown single crystal fiber having a longitudinal and lateralsize of 1 mm×1 mm and a length of 100 mm was elementary analyzed by EPMAwith respect to the composition distribution viewed in the lengthdirection (grown direction). As a result, it was found that, theproportion of neodymium in the composition of the single crystal fibercould be controlled to 1.0 mol % with an error of not more than ±2%which is a high precision within a detectable limit. From, Nd laseroscillation experiment, a three times or more of the output and a sharpwavelength property as compared with a sample prepared by a CZ methodwere obtained.

Example 8

Using the single crystal producing apparatus shown in FIGS. 22 and 23, aKLN single crystal fiber was produced according to the aforedescribedmethod. Potassium carbonate, lithium carbonate and niobium oxide werereciped in a mol ratio of 30:20:50 to prepare a raw material powder.Around 50 g of the raw material powder were charged in a meltingcrucible 101 made of platinum and the melting crucible 101 was set at adesired position in the furnace. The temperatures in the melting furnace99 was controlled by the heating devices 109A, 109B and 109C and thetemperature in the growing furnace 100 side was controlled by a heatingdevice 108. The temperature gradient in the vicinity of the singlecrystal growing section was controlled by the supply of electric powerto a nozzle portion 104 and heat-generation of the after-heater. Thesingle crystal fiber moving mechanism could pull down the single crystalfiber at a controlled uniform drawing rate of 2-100 mm/hr in thevertical direction.

The temperature in the melting furnace was controlled to a temperatureof 1,100°-1,200° C. to melt the raw material in the crucible. Thetemperature in the growing furnace 100 was uniformly controlled to atemperature of 500°-1,000° C. The crucible 101, the nozzle portion 104and the after-heater 107 were respectively supplied with a desiredelectric power to optimize the temperature thereof for performing thegrowth of the single crystal. At that time, the single crystal growingsection 26 could be controlled to a temperature of 1,050°-1,150° C. anda temperature gradient of 10°-150° C./mm.

The nozzle portion 104 had outer and inner cross-sections of circularshapes, an outer diameter of 1 mm, an inner diameter of 0.8 mm and alength of around 50 mm. The nozzle portion 104 was extended in thehorizontal direction from around the middle portion between the surfacelevel 21a of the melt in the crucible 101 and the bottom surface 102.The crucible 101 had a circular shape in plan view, a diameter of 30 mmand a height of 30 mm. At this state, the single crystal fiber waspulled downwardly at a pulling rate of 20 mm/hr in the a axial directionto find out that a good KLN single crystal fiber can be pulled down. Inthe same manner, the single crystal fiber can be pulled down in the caxial direction.

The thus grown single crystal fiber having a longitudinal and lateralsize of 1 mm×1 mm and a length of 100 mm was examined with respect tothe composition distribution viewed in the length direction (growndirection) in the same manner as in Example 4. The result of themeasurement shows that the wavelength was controlled within not morethan 1 nm. So, the composition of the single crystal fiber could becontrolled with a high precision of not more than 0.01 mol % ofcomposition, which is a high precision never attained before as a KLNsingle crystal. The wavelength conversion efficiency of the KLN singlecrystal fiber was substantially the same with the theoretical value withan error of not more than ±2% which is within the range of measurementalerror.

Example 9

In the same manner as in Example 8, a KLN single crystal fiber was grownexcept that a raw material feeding mechanism was used in the furnace,which intermittently feeds the raw material in the melting crucible.Also, a cutting mechanism was arranged below the furnace, whichintermittently cuts the single crystal fiber to a desired length tocontinuously grow the single crystal fiber.

With the progress of the growing of the single crystal fiber, the amountof the melt in the crucible was decreased. Here, the raw material powderwas fed in the melting crucible such that the liquid surface of the meltexists at a level about 0.5±0.1 mm higher than the distal end of thenozzle portion. In this way, a single crystal fiber of a length of 10 mwas continuously formed and the variation in the composition wasmeasured in the same manner as in Example 4. As a result, the variationin the composition of the single crystal fiber could be controlled tonot more than 0.01 mol % over the entire length of around 10 m.

Example 10

The growing of the single crystal was performed in the same manner as inExample 5 using the nozzle portion shown in FIG. 24 to succeed inpulling down a KLN single crystal plate of a thickness of 1 mm and awidth of 30 mm. The diameter expanded portion 94 was made of a platinumplate of a height of 3 mm, a width of 30 mm and a thickness of 1 mm. Thepassages 94b had respectively a width of 0.5 mm and a spacing of 3 mm.

With the progress of the growing of the single crystal plate, the amountof the melt in the crucible was decreased. Here, the raw material powderwas fed in the melting crucible such that the liquid surface of the meltexists at a level about 2.0±0.1 mm higher than the distal end of thenozzle portion. The SHG phase matched wavelength and the conversionefficiency were measured to obtain the same values as those of thesingle crystal fiber.

Example 11

The present invention was applied to a method of growing a singlecrystal of a solid solution of neodymium substituted LiNbO₃ in the samemanner as in Example 8. Neodymium oxide, lithium carbonate and niobiumoxide were reciped in a mol ratio of 1:49:50 to prepare a raw materialpowder. Around 50 g of the raw material powder were charged in a meltingcrucible 101 made of platinum. The temperature in the melting furnacewas controlled to a temperature of 1,250°-1,350° C. to melt the rawmaterial in the crucible 101. The temperature in the growing furnace 100was uniformly uncontrolled to a temperature of 500°-1,200° C. Desiredelectric powers were supplied to the melting crucible 101, the nozzleportion 104 and the after-heater 107 to optimize the temperaturegradient at the respective portion to perform the growth of the singlecrystal. At that time, the single crystal growth section could controlto a temperature of 1,200°-1,300° C. and a temperature gradient of10°-50° C./mm.

At this state, the single crystal fiber was pulled downwardly at apulling rate of 20 mm/hr to find out that a good single crystal fibercould be pulled down.

The thus grown single crystal fiber having a longitudinal and lateralsize of 1 mm×1 mm and a length of 100 mm was elementary analyzed by EPMAwith respect to the composition distribution of the single crystal fiberviewed in the length direction (grown direction). As a result, it wasfound out that, the proportion of neodymium in the composition of thesingle crystal fiber could be controlled to 1.0 mol % with an error ofnot more than ±2% which is a high precision within a detectable limit.From Nd laser oscillation experiment, a three times or more of theoutput and a sharp wavelength property as compared with a sampleprepared by a CZ method were obtained.

Comparative Example 1

Using a conventional growth apparatus, a KLN single crystal fiber assame that of Example 4 was produced. The amount of the raw materialpowder charged in the melting crucible was 50 mg. The melting cruciblewas made of platinum. The temperature in the space 10 of the upperfurnace 2 was adjusted to a temperature of 1,100°-1,200° C. to melt theraw material powder in the crucible. The temperature in the space 18 ofthe lower furnace 3 was uniformly controlled to a temperature of500°-1,000° C. Desired electric power was supplied to the meltingcrucible in an effort of controlling the growth and pulling down thesingle crystal from the intake hole or drawing hole. At this state, thesingle crystal fiber was drawn at a drawing rate of 20 mm/hr to obtain aKLN single crystal fiber.

The thus grown single crystal fiber having a longitudinal and lateralsize of 1 mm×1 mm and a length of 100 mm was examined with respect tothe composition distribution viewed in the length direction (growndirection) in the same manner as in Example 4. As a result, the SHGphase matched wavelength had a variation of 50 nm in the wavelengthwhich corresponds to a high variation of exceeding 1.0 mol % in thecomposition when calculated by conversion which is a practicallyunacceptable level.

Comparative Example 2

In Comparative Experiment 1, the raw material powder was periodicallysupplied to the melting crucible in an amount corresponding to theamounts of the components drawn and evaporated from the melting cruciblein an effort of continuously growing the single crystal fiber. However,once the raw material powder was supplied to the melting crucible, thethermal equilibrium state in the melting crucible was largelyunbalanced, so that the continuous growing of the single crystal fiberbecame impossible.

Comparative Example 3

In Comparative Experiment 1, a crucible of a larger size was used andthe amount of the raw material powder initially charged in the cruciblewas increased to 5 g. The temperatures in the whole furnace werecontrolled by the upper furnace and the lower furnace, and electricpower was supplied to the crucible to control the growth and the pullingdown of the single crystal from the drawing hole.

However, though a larger electric power had to be supplied to thecrucible to improve the melting of the raw material powder in thecrucible if the temperature in the upper furnace was adjusted to a lowtemperature of 500°-900° C., the larger output of the electric powerresulted in non-crystallization of the melt. Meanwhile, if a smallerelectric power was supplied to the crucible, the melt was solidifiedbefore the drawing thereof from the drawing hole. Thus, a condition forpulling down the single crystal could not be found.

In the meantime, if the upper furnace was controlled to a temperature ofnot less than 900° C., the temperature gradient necessary for thecrystallization could not be retained in the vicinity of the drawinghole which is the crystal growing point by the radiant heat from thefurnace body, so that the pulling of the single crystal fiber downwardlywas impossible also in this case.

Hereinafter, embodiments of the third aspect of the present inventionwill be explained in more detail with reference to the drawings.

FIG. 25 is a schematic cross-sectional view of the producing apparatusfor growing a single crystal. FIG. 26 is an enlarged schematiccross-sectional view of the single crystal growing furnace. FIGS. 27 (a)and 27 (b) are schematic cross-sectional views of the single crystalgrowing section.

A melting crucible 112 is disposed in the interior of the furnace body.The upper furnace 2 is arranged to enclose the crucible 112 and itsupper space 10. The upper furnace 2 has a heater 4A embedded therein. Anozzle portion 113 extends downwardly from the lower end of the crucible112 and an opening 113a is provided at the lower end of the nozzleportion. A crucible 115 for growing the single crystal is disposed atimmediate below an opening 113a of the nozzle portion 113. A singlecrystal growing crucible 115 is disposed at the neighbourhood of theboundary portion between the upper furnace 2 and the lower furnace 3.The lower furnace 3 is arranged to enclose the single crystal fiberdrawing portion and its surrounding space 18. The lower furnace 3 has aheater 4B embedded therein. Of course, such an arrangement of theheating furnace may be changed variously.

The melting crucible 112, the nozzle portion 113 and the single crystalgrowing crucible 115 are respectively made of a corrosion-resistantelectrically conductive material. An electrode of the electric powersource 22A is connected to a portion O of the melting crucible 112through a leading wire and the other electrode of the power source 22Ais connected to a portion P of the melting crucible 112. An electrode ofthe electric power source 22B is connected to the upper end T of thenozzle portion 113 and the other electrode of the power source 22B isconnected to the lower end Q of the nozzle portion 113.

Similarly, an electrode of the electric power source 22C is connected toan end portion R of the single crystal growing crucible 115 through aleading wire and the other electrode of the power source 22C isconnected to a portion S of the single crystal growing crucible 115.These electric power supplying mechanisms are separated from each otherand constructed to control its voltage independently. The after-heater66 is arranged below the single crystal growing crucible 115 in thespace 18.

In case if the temperature gradient of the nozzle portion is alreadyoptimized by the furnace body (the heat-generating member and therefractive material), the after-heater 66 is not indispensable and maybe omitted.

The temperature distributions in the spaces 10, 18 are suitablydetermined by the heat-generation of the upper furnace 2 and the lowerfurnace 3, the raw material for the melt is fed in the melting crucible112, and electric power is supplied to the melting crucible 112, thenozzle portion 113 and the single crystal growing crucible 115 to heatgenerate them respectively thereby to melt the raw material in themelting crucible 112 to form a melt 21. The melt 21 is flowed downthrough the passage 114 in the nozzle portion 113, while retaining itsmelted state by means of the heat-generation of the nozzle portion 113and the after-heater 66.

The melt is flowed in the single crystal growing crucible 115 from theopening 113a. The melt 116 is stayed in the single crystal growingcrucible 115.

Alternatively, the melt flowed from the opening 113a may be solidifiedat immediate below the opening 113a to assume a polycrystalline body,and the fiber or plate made of the polycrystalline body may becontinuously fed in the single crystal growing crucible 115 in which thefiber or plate may be melted.

At the stage before starting the pulling down of the single crystalfiber, the melt 116 is slightly protruded from the opening 118a at thesingle crystal growing section 117 existing at the end portion of thenozzle portion 113 and retained by its surface tension to form arelatively flat surface 121.

Different from the melting crucible 112 which performs the melting ofthe raw material, the single crystal growing crucible 115 does notperform the melting of the raw material and is smaller in size than themelting crucible 112. In the small crucible 115, the melt 116 is drawnby the surface tension along the shape of the vertical inner side wall115a and the bottom surface 115b to assume an inwardly recessed liquidussurface 120. Therefore, the gravity acting on the melt 116 in the nozzleportion 118 is largely decreased by the contact of the melt to the innerwall surfaces 115a and 115b of the single crystal growing crucible 115.

At this state, the seed crystal 27 is moved upwardly as shown by thearrow T to contact its upper end surface 27a with the lower surface 121of the melt 116. At that time, a uniform meniscus 122 is formed betweenthe upper end of the seed crystal 27 and the lower end of the melt 116drawn downwardly from the opening 118a of the nozzle portion 118.

As a result, a single crystal fiber 12 is continuously formed on theseed crystal 27 and pulled downwardly. In this embodiment, the seedcrystal 27 and the single crystal fiber 12 are pulled down by therollers 67.

Meanwhile, in case if the amount of the material powder supplied to thecrucible is increased according to a conventional method, an expandedportion of the melt is formed downwardly from the opening 118a of thecrucible. Moreover, if the weight of the material powder is large, themelt is flowed when the material powder is melt, and a good meniscuscannot be formed when the end surface 27a of the seed crystal 27 iscontacted with the melt.

FIG. 28 is a schematic cross-sectional view of another embodiment of theproducing apparatus for growing the single crystal showing the shape ofthe crucibles. In FIG. 28 the same functional members are allotted withthe same reference numerals as those of FIG. 25 and the sameexplanations are used.

The nozzle portion 113 extends downwardly from the lower end of themelting crucible 112 and has the opening 113a at the lower end. The meltor its solidified body is continuously fed from the opening 113a to thesingle crystal growing crucible 115.

The melting crucible 112 and the nozzle portion 113 are respectivelymade of a corrosion resistant material. The electrodes of the electricpower source 22A are connected to the upper end portion O and the lowerbent portion P. A circular heat-generating member 114 is arranged aroundthe nozzle portion 113. An electrode of the electric power source 22B isconnected to the upper end portion T of the heat-generating member 114and the other electrode of the electric power source 22B is connected tothe lower end Q of the heat-generating member 114. These electric powersupplying mechanisms are separated from each other and constructed tocontrol its voltage independently.

A radio frequency induction heating mechanism not shown may be providedaround the nozzle portion 113 to heat the same thereby to control thesupply of the melt.

In the above described embodiments, a circular shaped nozzle portion wasused as the nozzle portion of the melting crucible as well as as thenozzle portion of the single crystal growing crucible. However, such acircular shaped nozzle portion is generally much expensive inprocessing. For example, the nozzle portion having a small innerdiameter is difficult to produce by processing a material made of anoble metal, such as, platinum.

Therefore, the inventors produced the nozzle portion by forming a groovein a corrosion-resistant member made of a corrosion-resistant metal or acorrosion-resistant ceramics, and adhering or joining the grooved memberto the other corrosion-resistant member. In such a nozzle portion, thegroove serves as the elongated minute diameter passage for the melt. Thegrooved member should have a flat surface on the side in which thegroove is formed, and is preferably a flat plate shaped.

At that time, the passage for the melt may be prepared by forming thegroove in both the flat plates and integrally uniting the grooves whenadhering the flat plates. Alternatively, the passage may be prepared byforming the groove in one flat plate, while leaving the other flat plateas it is, and adhering the two flat plates to obtain the passage formedby the groove in the flat plate. The nozzle portion prepared in this waycan be used for the crucible for melting the raw material as well as forthe single crystal growing crucible.

In addition, in using the single crystal growing crucible the inventorscould produce a single crystal plate by forming a plurality of groovesin parallel to each other in the nozzle portion thereby to form thepassages for the melt, and drawing the melt from the passages.

If the nozzle portion is used for the single crystal growing crucible,preferably the grooves have respectively a width of 0.01-0.5 mm, and aspacing of 0.1-10 mm. The grooves may have a square, a rectangular,V-shape or a half circular shape.

Concretely explaining, an elongated flat plate 121 is prepared as shownin FIG. 29 (a), and an elongated groove 122 is formed longitudinally ina flat plate 121 as shown in FIG. 29 (b). The same work is effectedusing another flat plate 121. The two flat plates 121 are adhered facingthe grooves 122 to each other to prepare a nozzle portion 123 as well aspassages 124 in the nozzle portion 123 as shown in FIG. 29 (c).

The nozzle portion 123 is joined to the bottom 125a of the crucible 125and the melt is flowed down in the passages 124 as shown in FIG. 29 (d).If such a means is used, the nozzle portion for forming the singlecrystal fiber can easily be prepared. The crucible having such a nozzleportion may be used as the melting crucible as well as as the singlecrystal growing crucible.

Next, concrete shapes of the nozzle portion for producing the singlecrystal plate will be explained with reference to preferred embodiments.A plurality of elongated grooves 127 in parallel to each other areformed in a flat plate 126 as shown in FIG. 30 (a). The same work iseffected using another flat plate 126. The two flat plates 126 areadhered facing the grooves 127 to each other to prepare a flat shapednozzle portion 128 as well as a plurality of passages 130 in the nozzleportion 128 as shown in FIG. 30 (b). The reference numeral 129 denotes ajoint.

The nozzle portion 128 is joined to the bottom of a rectangular meltingcrucible 131 as shown in FIG. 30 (c). The melt 21 in a crucible 131flows down in the respective passage 130 of the nozzle portion 128 toflow out from the lower end of the respective passage 130. At that time,the melt flowed out from the lower end of the respective passage 130becomes integral and flowed on the bottom plate 128a of the nozzleportion 128, and the integral flow of a shape of a plate 132 made of themelt or the polycrystalline is fed to the single crystal growingcrucible.

In the embodiment shown in FIG. 31, a plurality of tubular members 134are used as the respective nozzle portion and arranged such that theirouter circumferential surfaces continue from each other. Though thecrucible portions were omitted in FIG. 31, a crucible, such as, thecrucible 131 as shown in FIG. 30 (c) may be used. The tubular members134 have therein respectively a passage 133 for the melt and has anopening at the lower bottom end surface 134a thereof.

The melt in the crucible flows down in the respective passage 133 of therespective tubular nozzle portions 134 and flowed out therefrom. At thattime, the melt flowed from the respective passage 133 is made integraland flowed on the bottom end surface 134a of the nozzle portions 134 tobecome a flat plate 132 and fed to the single crystal growing crucible.

A nozzle portions of the same shape but shorter length could be used asthe nozzle portion of the lower single crystal growing crucible tostably produce a single crystal plate similarly as in the case of theabove described single crystal fiber.

Hereinafter, the present invention will be explained with reference tomore concrete experimental results.

Example 12

Using the single crystal producing apparatus shown in FIG. 25, a KLNsingle crystal fiber was produced according to the present invention.The temperatures in the whole furnace were controlled by means of theupper furnace 2 and the lower furnace 3. The temperature gradient in theneighbourhood of the single crystal growing section was controlled bythe supply of electric power to the single crystal growing crucible 115and heat-generation of the after-heater 66. For pulling down the singlecrystal fiber a mechanism was used which pulls the single crystal fiberdownwardly at a controlled uniform pulling rate in a range of 2-100mm/hr in the vertical direction.

Potassium carbonate, lithium carbonate and niobium oxide were reciped ina mol ratio of 30:20:50 to prepare a raw material powder. Around 50 g ofthe material powder were fed in the melting crucible 122 made ofplatinum and the melting crucible 122 was set at a desired position inthe furnace. The nozzle portion 113 had outer and inner cross-sectionsof circular shapes and an outer diameter of 1 mm, an inner diameter of0.3 mm and a length of 20 mm. The melting crucible had a circular shapein plan view and a diameter of 30 mm and a height of 30 mm. The singlecrystal growing crucible had a size capable of containing 1 g of the rawmaterial. A tube of an outer diameter of 1.2 mm, an inner diameter of0.8 mm and a length of 2 mm were used for the nozzle portion.

The temperature in the space 10 of the upper furnace 2 was adjusted to atemperature of 1,100°-1,200° C. to melt the raw material in the crucible112. The temperature in the space 18 of the lower furnace 3 wasuniformly controlled to a temperature of 500°-1,000° C. Desired electricpowers were supplied to the melting crucible and the nozzle portion tocontrol the supply of the melt to the single crystal growing crucible115. Electric power was controlledly supplied to the after-heater 66 andthe single crystal growing furnace. As a result, the single crystalgrowing section could be controlled to a temperature of 1,050°-1,150° C.and to a temperature gradient of 10°-150° C./mm.

At this state, the single crystal fiber was pulled downwardly at apulling rate of 20 mm/hr to find out that a good KLN single crystalfiber could be drawn down.

The thus grown single crystal fiber having a longitudinal and lateralsize of 1 mm×1 mm and a length of 100 mm was examined with respect tothe composition distribution of the single crystal fiber viewed in thelength direction (grown direction). Concretely explaining, the singlecrystal fiber was irradiated at various portions in the longitudinaldirection by a light beam, and the wavelength of the light beam emittedtherefrom was measured to detect an SHG phase matched wavelength. Ifthere is even a slight variation in the composition of the KLN singlecrystal fiber, the SHG phase matched wavelength of the emitted lightbeam is varied by the variation in the composition.

The result of the measurement shows that the wavelength was controlledwithin not more than 1 nm. So, the composition of the single crystalfiber could be controlled with a high precision of not more than 0.01mol % of composition, which is a high precision never attained before asa KLN single crystal. The wavelength conversion efficiency of the KLNsingle crystal fiber was substantially the same with the theoreticalvalue with an error of not more than ±2% which is within the range ofmeasuremental error.

Example 13

In the same manner as in Example 12, a KLN single crystal fiber wasgrown except that a raw material feeding mechanism was used in thefurnace, which intermittently feeds the raw material in the meltingcrucible 112. Also, a cutting mechanism was arranged below the furnace,which intermittently cuts the single crystal fiber to a desired lengthto continuously grow the single crystal fiber. With the progress of thesingle crystal fiber, the raw material powder was periodically fed inthe melting crucible in an amount corresponding to the amounts of thecomponents pulled down out and evaporated from the melting crucible. Inthis way, a single crystal fiber of a length of around 10 m wascontinuously formed and the variation in the composition thereof wasmeasured in that same manner as in Example 12. As a result, thevariation in the composition of the single crystal fiber could becontrolled within not more than 0.01 mol % over the entire length ofaround 10 m.

Example 14

The nozzle portion 128 and the crucible 131 as shown in FIG. 30 wereused to succeed in pulling down a KLN single crystal plate of athickness of 1 mm and a width of 30 mm. However, a platinum plate of asize of 30 mm×30 mm×0.6 mm was used as the plate 126. Grooves 127 eachhaving a width of 0.1 mm were formed with a spacing of 5 mm in theplatinum plate 126 by mechanical cutting using a dicing machine. A plateshaped nozzle portion of a thickness of 1.2 mm was prepared by joiningtwo sheets of the platinum plate. Parallely arranged tubular nozzles asshown in FIG. 31 consisting of 30 tubes of an outer diameter of 1 mm andan inner diameter of 0.6 mm and a length of 2 mm parallely arranged in arow were used as the nozzle portion of the single crystal growingcrucible. The melt was flowed from the passages of the melt as explainedabove with reference to FIGS. 30 (a) and (c). The SEG phase matchedwavelength and the wavelength conversion efficiency in the interior ofthe single crystal plate were measured to obtain the same values as inthe case of the above described single crystal fiber.

Example 15

The present invention was applied to a method of growing a singlecrystal of neodymium substituted in LiNbO₃. However, the amount ofsubstituted neodymium in this system was around 0.3 mol %, if a method,for example, a CZ method was used.

Neodymium oxide, lithium carbonate and niobium oxide were reciped in amol ratio of 1:49:50 to prepare a raw material powder. The sameapparatus as in Example 12 for producing a single crystal fiber wasused. Around 50 g of the material powder were fed in the meltingcrucible 112 and the melting crucible 112 was set at a desired positionin the furnace. The temperature in the space 10 of the upper furnace 2was adjusted to a temperature of 1,250°-1,350° C. to melt the rawmaterial in the melting crucible 112. The temperature in the space 18 ofthe lower furnace 3 was uniformly controlled to a temperature of500°-1,200° C. The temperature gradient in the neighbourhood of thesingle crystal growing section was controlled by the supply of electricpower to the nozzle portion 113, the single crystal growing furnace 115and the heat-generation of the after-heater 66.

At that time, the single crystal growing section was controlled to atemperature of 1,200°-1,300° C. and to a temperature gradient of10°-150° C./mm. At this state, the single crystal fiber was pulleddownwardly at a pulling rate of 20 mm/hr to find out that a good KLNsingle crystal fiber could be pulled down.

The thus grown single crystal fiber having a longitudinal and lateralsize of 1 mm×1 mm and a length of 100 mm was elementary analyzed by RPMAwith respect to the composition distribution of the single crystal fiberviewed in the length direction (grown direction). As a result, it wasfound that, the proportion of neodymium in the composition of the singlecrystal fiber could be controlled to 1.0 mol % with an error of not morethan ±2% which is a high precision within a detectable extent.

Also, the comparative experiments 1, 2 and 3 same as described abovewere repeated.

Hereinafter, embodiments of the fourth aspect of the present inventionwill be explained.

In the fourth aspect of the present invention, more preferably a laserbeam is irradiated to an oxide series single crystal having the effectof second harmonic generation and detected the SHG wave generation. Assuch an oxide series single crystal, use may be made of publicly knownoxide series single crystals. Particularly preferable are those, suchas, KLN, KLTN, or KN, etc., which generates a blue light beam by SHG orthose, such as, CLBO, BBO, LBO, etc., which generates a ultra violetray. Of course, the present invention is applicable to a more higherdegree of wavelength conversion, such as, a third harmonic wave, or afourth harmonic wave.

If the laser beam irradiated to the oxide series single crystal has arange of wavelength including a wavelength corresponding to the purposedcomposition, the emitted light beam from the oxide series single crystalmay be analyzed by a spectrum analyzer to detect the respectiveintensity of the respective wavelength in the desired range ofwavelength.

Concretely explaining, assuming that the light beam corresponding to thepurposed composition has a wavelength λ0 and the laser beam has lightbeams of wavelengths between λ1 and λ2 in FIG. 32, the intensities ofthe laser beams between the wavelengths λ1 and λ2 are detected by aspectrum analyzer. If the oxide series single crystal pulled down fromthe drawing hole of the crucible has a desired composition, the laserbeam has a maximum value V at the wavelength λ0. However, with theprogress of the production, the thermal state of the oxide series singlecrystal at the drawing hole and the effect of gravity, etc., are alittle changed, and the peak wavelength λ0 is shifted little towards thewavelength direction of λ1 or λ2. Accompanying to such a shifting, thewhole of the curve W is shifted little to the direction of the arrow Yor the arrow H in the graph.

Therefore, at the stage of pulling down the oxide series single crystal,if the composition of the single crystal is varied then the peakwavelength of the emitted light beam may be varied. So, the change ofthe peak wavelength may be detected immediately and feed backed to theraw material feeding device.

If the light beam receiving device can not detect the distribution ofthe wavelength components as a photodiode, the intensity of the emittedlight beam of the respective wavelength can not be detected directly.Therefore, a preferable monitoring method in such a case will beexplained with reference to FIG. 33.

The wavelength of the emitted light beam corresponding to the purposedcomposition is assumed as λ0. If the composition of the oxide seriessingle crystal pulled down from the drawing hole of the crucible meetsthe purposed composition, the intensity of the laser beam has themaximum value V at the wavelength λ0. With the progress of theproduction, the peak wavelength λ0 is shifted little to λ4 or λ5 asdescribed above. Accompanying to such a shifting, the curve W isdisplaced little to the direction of right or left to become the curve Zor the curve S.

However, the shifting of the maximum value is little, and moreover theshape of the whole curve has usually a very small inclination at aroundthe maximum value. Therefore, it has been found out that, if the maximumvalue of the curve is displaced little, the variation of the emittedlight beam at the peak wavelength λ0 becomes further small, so that thedetection of the variation in the composition is practically impossible.

Thus, the oxide series single crystal was irradiated by a first laserbeam having a wavelength 2λ7 larger than a wavelength 2λ0 and a secondlaser beam having a wavelength 2λ6 smaller than a wavelength 2λ0, andthe intensity of the respective emitted light beam corresponding tothese first and second laser beams were measured by a light beamreceiving device.

As a result, if the composition of the oxide series single crystalpulled down from the drawing hole of the crucible meets the purposedcomposition, the emitted light beam has an intensity p₀ at thewavelength λ6 and an intensity q₀ at the wavelength λ7. With theprogress of the production, if the peak value λ0 is shifted to thedirection of λ5, the curve W is displaced to the right to become a curveZ. At this time, the emitted light beam has a decreased intensity p₁ atthe wavelength λ6 which is a smaller value than p₀. Meanwhile, theemitted light beam has an increased intensity q₁ at the wavelength λ7which is a larger value than q₀. In contrast, if the peak value λ0 isdisplaced to the direction of λ4, the curve W is displaced to the leftto become a curve S. At this time, the emitted light beam has aincreased intensity p₂ at the wavelength λ6 which is a larger value thanp₀. Meanwhile, the emitted light beam has an decreased intensity q₂ atthe wavelength λ7 which is a smaller value than q₀.

In this way, the increasement and the decreasement of the intensityoccurs as a pair at the both wavelength sides of the curve, so that anextremely good sensibility against a variation in the composition can beobtained. Moreover, if the emitted light beams are measured at selectedwavelengths which are outside of the peak wavelengths λ0, λ4 and λ5while avoiding the peak wavelengths λ0, λ4 and λ5, the relatively largeinclined portions of the curve can be utilized, so that a particularlysharp sensibility can be obtained also from this point of aspect.

In the aforedescribed method, the first and second laser beams maysimultaneously be used to irradiate the single crystal. Alternatively, alaser device capable of varying the wavelength may be used tosequentially irradiate the single crystal two times using laser beams oftwo types of wavelength.

In the present invention, preferably the size of the cross-section ofthe oxide series single crystal is measured by an optical sensor. Ingrowing the single crystal, the shape of the cross-section is usuallycontrolled to a constant and the precision of the control can beimproved by measuring the size precisely and cancelling the variation inthe light beams-permeating thickness.

Next, preferable embodiments of the present invention will be explainedin more detail. The inventors have made researches on using enlargedcrucibles in an effort of establishing a mass production technique by μpulling down process of pulling down the oxide series single crystal andtried in this process to use an enlarged crucible having a nozzleportion extending downwardly from the crucible and a single crystalgrowing section arranged at the lower end of the nozzle portion tocontrol the temperatures of the crucible and the single crystal growingsection independently from each other.

As a result, the inventors have found out that the oxide series singlecrystal could easily be drawn down continuously even when a large amountof the raw material powder of more than 5 g was melted in the meltingcrucible of an enlarged capacity meeting the increased amount of the rawmaterial powder.

A reason why such a function and effect were obtained is presumed thatthe single crystal growing section became difficult to directly receivethe influence of the heat generated by the melt in the crucible by theprovision of the single crystal growing section at the lower end of thenozzle portion, and simultaneously that the temperature gradient at theneighborhood of the single crystal growing section could be made largeby separately controlling the temperature of the crucible and thetemperature of the single crystal growing section and or the nozzleportion.

Moreover, the inventors have found out that, according to this method,the variations in the composition of the KLN single crystal fiber couldbe reduced to a surprisingly high precision of not more than 0.01 mol %,even when the amount of the raw material powder melted in the cruciblewas increased to an amount of around 30-50 g. Therefore, the oxideseries single crystal of such an extremely high precision can be massproduced by combining the producing method and the present invention.

In addition, the inventors have made researches on the state of the meltin the single crystal growing section and the physical properties of thesingle crystal. As a result, the inventors have found out that a goodoxide series single crystal of a very few variation in the compositioncould be pulled down continuously in case when the surface tension isdominant than the gravity in the environment of the single crystalgrowing section. This is considered presumably due to a reason that agood meniscus was formed thereby.

In this way, in order to create a condition that the surface tension ismore dominant than the gravity in the single crystal growing section,the provision of a mechanism in the crucible of decreasing the gravityacting on the melt in the nozzle portion is effective. The inventorshave made researches on such a mechanism to find out that, by decreasingthe inner diameter of the nozzle portion to not more than 0.5 mm, thecondition that the surface tension is dominant than the gravity actingon the melt can be created in the nozzle portion to form a uniformmeniscus at the distal end opening of the nozzle portion.

However, if the inner diameter of the nozzle portion is less than 0.01mm, the growing speed of the single crystal becomes too slow, so thatthe inner diameter is preferably not less than 0.01 mm from the viewpoint of mass production. An optimum inner diameter of the nozzleportion is in a range of 0.01-0.5 mm and varies a little depending onthe viscosity, the surface tension and the specific gravity of the melt,and the growing speed of the single crystal, etc.

In addition, the inventors have made researches on this point to obtainthe following finding. That is, in the conventional μ pulling downprocess presumably the single crystal fiber could have been pulled downcontinuously by virtue of the small scale of the crucible, and this ispresumably because the amount of the melt in the crucible was small andthe melt adhered on the inner wall of the crucible by its surfacetension to relatively reduce the gravity acting on the drawing hole sothat a meniscus which is uniform to a certain extent could be formed.However, when a crucible of an enlarged size was used, such conditionthat the surface tension was dominant at around the drawing hole waslost.

Moreover, in this method, the temperature gradient viewed in thelongitudinal direction of the nozzle portion can easily be made large atthe neighbourhood of the single crystal growing section thereby toquench the melt flowed down in the nozzle portion.

Therefore, the method is particularly suitable for producing the singlecrystal of a solid solution state. The single crystal of a solidsolution state has a property that the proportion of its composition isvaried in an eqiliblium condition. When the conventional μ pulling downprocess was used for producing the single crystal of a solid solutionstate, the melt was in the eqiliblium condition at the drawing hole, sothat the composition of the solid solution could have been varied by aslight change of the temperature and the speed of the solidification dueto such a property. In contrast, according to the present method andapparatus, the quenching of the single crystal of a solid solution ispossible at the neighbourhood of the single crystal growing section, sothat the composition of the melt can be retained.

Illustrative examples of such an oxide series single crystal of a solidsolution state are, for example, Mn-Zn ferrite, tungsten bronzestructures around Ba_(1-x) Sr_(x) Nb₂ O₆, KLN, KLTN K₃ Li_(2-2x) (Ta_(y)Nb_(1-y))_(5+x) !O_(15+x), etc.

When the raw material powder is supplied to the crucible, the thermalstate in the crucible is varied due to the heat of solution of the rawmaterial thereby to cause variations in the composition of the singlecrystal to occur. However, if the nozzle portion is provided below thecrucible as described above, the raw material can be supplied to thecrucible continuously or intermittently. This is because, if theaforedescribed thermal variation is occurred in the crucible, it affectsfew thermal influence over the single crystal growing section, and thesingle crystal growing section is not in an equilibrium state but in akinetic theory state so that the single crystal growing section isfurther not affected by the influence of the thermal variations.

In the present invention, heating method of the crucible is notparticularly limited. However, the heating furnace is preferablyarranged to surround the single crystal growing device. At that time,preferably the heating furnace is divided into an upper furnace and alower furnace, the crucible is surrounded by the upper furnace and theupper furnace is heat-generated to a relatively high temperature toassist the melting of the material powder in the crucible. Meanwhile,preferably the lower furnace is arranged around the nozzle portion andheated to a relatively lower temperature to make the temperaturegradient large in the single crystal growing section at the lower end ofthe nozzle portion.

In addition, in order to improve the efficiency of melting the rawmaterial powder in the crucible, preferably the crucible per se is madeof an electrically conductive material and heated by the supply ofelectric power thereto rather than by heating the crucible solely by theheating furnace. In addition, in order to retain the melted state of themelt flowing in the nozzle portion, preferably the nozzle portion ismade of an electrically conductive material and heat-generated bysupplying electric power thereto.

Particularly, in order to enlarge the temperature gradient in the singlecrystal growing section, preferably the electric power supplyingmechanism to the crucible and the electric power supplying mechanism tothe nozzle portion are separated from each other so that they can becontrolled independently.

As such an electrically conductive material, platinum, platinum-goldalloys, platinum-rhodium alloys, platinum-iridium alloys, and iridiumare preferable particularly from the aspect of the corrosion resistantproperty.

However, platinum and the like electrically conductive material haverespectively a relatively low resistivity, so that the thickness of thenozzle portion has to be made small to make its resistivity larger thana certain extent in order to effectively heat it by supplying anelectric power thereto. For example, if the nozzle portion is made ofplatinum, it had to be made of a thin film of a thickness of around100-200 μm. However, if the nozzle portion is made of such a thin film,the nozzle portion becomes weak in structure and is easily deformed, sothat the stable production of the single crystal is likely obstructed.

So, in order to effectively heat the nozzle portion, a heat-generatingresistive member may be provided around the nozzle portion andheat-generated by supplying electric power thereto. In such a case, thenozzle portion may be made of a corrosion-resistant material asdescribed above and heat-generated by supplying electric power theretoor it may not be supplied by electric power. By affording a principalheating function to the heat-generating resistive member surrounding thenozzle portion in this way, the load of heat-generation required to thenozzle portion becomes small, and the nozzle portion may not necessarilybe heat-generated. Thus, the nozzle portion can have a larger thicknessof e.g. not less than 300 μm to achieve an improved mechanical strength,so that it may suit to the mass production.

The present invention is also satisfactorily applicable not only to theproduction of the single crystal fiber but also to the production of thesingle crystal plate. Concrete method of forming the plate will beexplained below.

The property of the KLN single crystal were described above.

FIG. 34 is a schematic cross-sectional view of an embodiment of thefourth aspect of the present invention showing a producing apparatus forgrowing the single crystal, and FIGS. 3 (a) and 3 (b) are schematiccross-sectional views thereof for explaining the distal end portion ofthe nozzle portion.

The crucible 20 is disposed in the interior of the furnace body. Theupper furnace 2 is arranged to surround the crucible 20 and its upperspace 10 and has the heater 4A embedded therein. The nozzle portion 25extends downwardly from the lower end of the crucible 20 and has theopening 25a at the lower end. The lower furnace 3 is arranged tosurround the nozzle portion 25 and its surrounding space 18 and has theheater 4B embedded therein. Of course the shape per se of such a heatingfurnace may be changed variously. For example, though the heatingfurnace was divided into two heating zones in FIG. 34, the heatingfurnace may be divided into at least three heating zones. The crucible20 and the nozzle portion 25 are respectively made of acorrosion-resistant electrically conductive material.

An electrode of the electric power source 22A is connected to a portionB of the crucible 20 through a leading wire 68 and the other electrodeof the power source 22A is connected to a lower bent edge portion C ofthe crucible 20. An electrode of the electric power source 22B isconnected to a portion D of the nozzle portion 25 through a leading wire68 and the other electrode of the power source 22B is connected to alower end E of the nozzle portion 25. These electric power supplyingmechanisms are separated from each other and constructed to control itsvoltage independently.

In addition, the after-heater 66 is arranged in the space 18 to surroundthe nozzle portion 25 with a spacing. The intake tube 23 extendsupwardly in the crucible 20 and has the intake hole 24 at the upper end.The intake hole 24 is a little protruded from the bottom of the melt 21.

The intake hole 24 may be arranged at the bottom of the crucible 20 suchthat it does not protrude from the bottom of the crucible 20. In such acase, the intake tube 23 is not arranged. However, if the crucible 20 isused for a prolonged period of time, the impurities in the melt areoccasionally gradually accumulated at the bottom of the crucible 20. Byproviding the intake hole 24 at the upper end of the intake tube 23 asin the present invention, the impurities accumulated at the bottom ofthe crucible 20 are hardly introduced in the intake hole 24, because theintake tube 23 is protruded from the bottom of the crucible 20.

The temperature distributions in the spaces 10, 18 are suitablydetermined by the heat-generation of the upper and lower furnaces 2 and3, the raw material is fed in the melting crucible 20, and the meltingcrucible 20 and the nozzle portion 25 are heat-generated by supplyingelectric power thereto. At this state, the melt 21 is slightly protrudeddownwardly from the opening 25a in the single crystal growing section 26existing at the lower end of of the nozzle portion 25 and retained byits surface tension to form a relatively flat surface 29.

The gravity acting on the melt in the crucible 20 is largely decreasedby the contact of the melt with the inner wall surface of the nozzleportion 25. Particularly, by using the nozzle portion 25 of an innerdiameter of not more than 0.5 mm, a uniform meniscus could be formed.

At this state, the seed crystal 27 is moved upwardly to contact itsupper end surface 27a with the lower end surface 29 of the melt 21.Then, the seed crystal 27 is pulled downwardly as shown in FIG. 3 (b).At that time, a uniform meniscus 30 is formed between the upper end ofthe seed crystal 27 and the lower end surface 29 of the melt 21 drawndownwardly from the nozzle portion 25.

As a result, a single crystal fiber 12 is continuously formed on theseed crystal 27 and pulled downwardly. In this embodiment, the singlecrystal fiber 12 is pulled down by the driven rollers 67.

Meanwhile, in case if the amount of the material powder supplied to theconventional crucible is increased, an expanded portion of the melt isformed downwardly from the drawing hole of the crucible. If the upperend surface 27a of the seed crystal 27 is contacted to the melt 21 atthis state, a good meniscus is not formed.

If the single crystal fiber is continuously pulled downwardly, thesingle crystal fiber 12 is irradiated by a laser beam of a wavelength ofaround 2λ2 from a laser beam source 136 as shown by the arrow 139 andthe emitted light beam 141 of a wavelength of around λ2 from the singlecrystal fiber 12 by second harmonic generation is received by a lightbeam-receiving device 137C through a long wavelength cut filter 142 tomeasure the intensity thereof. A signal from the light beam-receivingdevice 137C is transmitted to a controlling device 144 through a signalwire 143 and treated therein to control the proportion of thecomposition of the raw material to be charged in the crucible 20 from anupper raw material feeding device 145. If the measured intensity of theemitted light beam is varied from the purposed value, a signal forchanging the proportion of the composition of the raw material istransmitted from the controlling device 144 to the feeding device 145 toattain a feed back.

In order to control more precisely, reflecting mirrors 139, 140 andlight beam-receiving devices 137A, 137B may be combined to transmitrespective signal as to a portion of a long wavelength of around 2λ0 tothe controlling device 144 through the signal wire 143.

Hereinafter, more concrete experimental results will be described.

Example 16

Using the single crystal producing apparatus shown in FIG. 34, a KLNsingle crystal fiber was produced according to the present invention.The temperatures in the whole furnace were controlled by means of theupper furnace 2 and the lower furnace 3. The temperature gradient in theneighbourhood of the single crystal growing section was controlled bythe supply of electric power to the nozzle portion 25 andheat-generation of the after-heater 66. For pulling down the singlecrystal fiber a mechanism was used which pulls the single crystal fiberdownwardly at a controlled uniform pulling rate in a range of 2-100mm/hr in the vertical direction. As the laser beam source 136, a tunabletitanium sapphire laser beam source was used which can generate thelaser beam in a wavelength range of 780-900 nm.

Potassium carbonate, lithium carbonate and niobium oxide were reciped ina mol ratio of 30:20:50 to prepare a raw material powder. Around 50 g ofthe material powder were fed in the melting crucible 20 made of platinumand the melting crucible 20 was set at a desired position in thefurnace. The temperature in the space 10 of the upper furnace 2 wasadjusted to a temperature of 1,100°-1,200° C. to melt the raw materialin the crucible 20. The temperature in the space 18 of the lower furnace3 was uniformly controlled to a temperature of 500°-1,000° C. Desiredelectric powers were supplied to the melting crucible 20, the nozzleportion 25 and the after-heater 66 to perform the growing of the singlecrystal. At that time, the single crystal growing section could becontrolled to a temperature of 1,050°-1,150° C. and to a temperaturegradient of 10°-50° C./mm.

The nozzle portion 25 had an outer and inner cross-sections of circularshapes and an outer diameter of 1 mm, an inner diameter of 0.1 mm and alength of 20 mm. The melting crucible 20 had a circular shape in planview and a diameter of 30 mm and a height of 30 mm. At this state, thesingle crystal fiber was pulled downwardly at a pulling rate of 20mm/hr.

Simultaneously, the single crystal fiber was irradiated by a laser beamof nearly a purposed phase matched wavelength of 850 nm from a titaniumsapphire laser beam source and the light beam emitted therefrom wasanalyzed by a spectrum analyzer. As the raw material, powders of thefollowing two types of composition were used.

Powder 1: K₃.1 Li₂ Nb₅ O

Powder 1: K₂.9 Li₂ Nb₅ O

Initially, the powder 1 and the powder 2 were mixed in a ratio of 1:1and the mixture was charged in the crucible. Then the amount of thepowder 1 in the mixture was increased, if the peak wavelength of theemitted light beam is moved to a longer direction, while the amount ofthe powder 2 in the mixture was increased, if the peak wavelength of theemitted light beam is moved to a shorter direction.

In this way, a single crystal fiber of a longitudinal and lateral sizeof 1 mm×1 mm and a length of 100 mm was continuously grown, whilecontrolling the mixing proportion of the raw material. As a result, thesingle crystal fiber could emit a light beam of a phase matchedwavelength with a small error of not more than 0.2 nm, so that thecomposition of the single crystal fiber could be controlled with a smallerror of not more than 0.01 mol %, which is a much high precision neverbefore attained by a KLN single crystal.

Example 17

In the same manner as in Example 16, a KLN single crystal fiber wasproduced except that a severing device for intermittently severing thesingle crystal fiber to a desired length was arranged below the furnacefor continuously growing the single crystal fiber. With the progress ofthe growing of the single crystal fiber, the raw material powder wasperiodically fed in the melting crucible in an amount corresponding tothe amounts of the components drawn and evaporated from the meltingcrucible 20. At that time, the mixing proportion of the raw materialpowders was determined as described above.

In this way, a single crystal fiber of a length of around 10 m wascontinuously formed and the phase matched wavelength of the light beamemitted from the single crystal fiber could be controlled with an errorof not more than 0.2 nm, namely, the variation in the compositionthereof could be controlled with an error of not more than 0.01 mol %.

Example 18

Using the aforedescribed nozzle portion 25 and an elongated shape forthe nozzle portion 25, the inventors could succeed to pull down a KLNsingle crystal plate of a thickness of 0.3 mm.

In this case, the charge of the raw material powder was controlled byobserving changes of emitted light beams from two types of semiconductorlaser. A laser beam source 147A which generates a laser beam of awavelength of 2λ6 (848 nm, namely, 424 nm×2) against the purposedwavelength λ0 (425 nm), and a laser beam source 147B which generates alaser beam of a wavelength of 2λ7 (852 nm, namely, 426 nm×2) wereprepared. Light beam-receiving devices 148A, 148B which respectivelycorresponds to the respective laser beam source were disposed at theopposing positions to the laser beam sources so as to sandwich a singlecrystal plate 146 therebetween as shown in FIG. 35.

Even if the wavelength of the purposed wavelength λ0 varies 0.2 nm fromthe wavelength 425 nm by the variation in the composition of the singlecrystal, the intensity of the emitted light beam changes and the outputfrom the light receiving devices 148A, 148B changes. Therefore, thechanges of the outputs were transmitted to a controlling device 149 andfeed backed to control the mixing proportion of the raw material powderthrough the controlling device 144 thereby to control the growing of thesingle crystal. Because the phase matched half width of the secondharmonic wave changes depending on the thickness and the quality of thesingle crystal, the wavelength of the laser beam from the laser beamsource has to be selected. Because the KLN single crystal has atheoretical width of 3.5 nm at a thickness of 0.3 mm, the aforedescribed2λ6 and 2λ7 were selected. In case if the KLN single crystal has athickness of 0.6 mm, 2λ6 (849 nm, namely, 424.5 nm×2) and 2λ7 (851 nm,namely, 425.5 nm×2) may be used for the controlling.

Of course, by such a controlling method, the mixing proportion of theraw material powder may be controlled by feed backing also in the caseof the single crystal fiber.

Although the present invention was explained with reference to specificpreferable embodiments in the foregoing descriptions, it should beunderstood that the specific descriptions are merely for illustrationbut not for limiting the present invention, and the present inventioncan be put into practice by another ways without departing from thebroad spirit and scope of the present invention as defined in theappended claims.

What is claimed is:
 1. A process for continuously producing singlecrystals products, comprising the steps of:drawing downwardly a melt ofa single crystal raw material through a nozzle extending from a cruciblecontaining the melt, said nozzle having a single crystalgrowing-section, whereby a single crystal body is grown from the meltalong the single crystal growing-section; continuously downwardly movingthe single crystal body; and continuously forming a plurality of singlecrystal products by intermittently cutting the single crystal body beingdownwardly moved.
 2. An oxide-series single crystal producing processcomprising the steps of initially charging a raw material for theoxide-series single crystal in a crucible, melting the raw material inthe crucible, bringing a seed crystal into contact with the melt, andgrowing an oxide-series single crystal body while the melt is beingdownwardly drawn, wherein; said process is carried out by using aproducing apparatus including the crucible, a nozzle portion extendingfrom the crucible, and a downwardly directed single crystal-growingsection at a distal end of the nozzle portion, and (ii) a temperature ofthe crucible and a temperature of the single crystal-growing section areindependently controlled.
 3. The oxide-series single crystal producingprocess claimed in claim 2, further comprising a step of continuously orintermittently feeding the raw material in the crucible after theinitial charging of the raw material.
 4. The oxide-series single crystalproducing process claimed in claim 3, wherein a laser beam is irradiatedupon the oxide-series single crystal body, an output light beam from theoxide-series single crystal body is measured, and a composition ratio ofthe raw material to be fed to the crucible is controlled based on themeasured output light beam result.
 5. The oxide-series single crystalproducing process claimed in claim 2, wherein a surface tension of themelt is more dominant than the force of gravity acting on the melt inthe single crystal-growing section.
 6. The oxide-series single crystalproducing process claimed in claim 2, wherein said nozzle portionextends downwardly from the crucible, and the single crystal-growingsection is provided in a lower end portion of the nozzle portion.
 7. Theoxide-series single crystal producing process claimed in claim 2,wherein said nozzle portion is provided at a side face of the cruciblethereby forming a joint portion between the crucible and the nozzleportion, and a part of the nozzle portion extends above the jointportion between the crucible and the nozzle portion.
 8. The oxide-seriessingle crystal producing process claimed in claim 7, wherein a height ofthe nozzle portion is taken as a zero reference point, and a surfacelevel of the melt inside the crucible is not less than -10 mm and notmore than 50 mm with respect to the zero reference point.
 9. Theoxide-series single crystal producing process claimed in claim 2,wherein the melt is being drawn downwardly thereby continuously growingthe oxide-series single crystal body while fresh single crystal rawmaterial is periodically or continuously fed into the crucible.
 10. Theoxide-series single crystal producing process claimed in claim 2,wherein said oxide-series single crystal body has a planar shape, adistal end face of said nozzle portion has a flat surface having shapecorresponding to a cross sectional shape of the planar single crystalbody, plural rows of melt flow passages are formed in the nozzle portionand opened to said flat surface of the distal end face thereof, the meltis simultaneously drawn downwardly through said melt flow passages, andthe melts thus drawn downwardly through the respective melt flowpassages are integrally combined together along said flat surface toform said planar single crystal body.
 11. The oxide-series singlecrystal producing process claimed in claim 2, wherein said oxide-seriessingle crystal body has a solid-solution composition.
 12. Theoxide-series single crystal producing process claimed in claim 2,wherein said oxide-series single crystal body has a segregatedcomponent.
 13. An oxide-series single crystal-producing processcomprising the steps of melting a raw material for an oxide seriessingle crystal in a melting crucible; continuously feeding the melt ofthe raw material to a single crystal-growing crucible having a volumesmaller than that of the melting crucible through an opening provided inthe melting crucible; contacting a seed crystal to the melt at a drawinghole provided at the single crystal-growing crucible; and growing anoxide-series single crystal body, while drawing the melt downwardly. 14.The oxide-series single crystal-producing process claimed in claim 13,wherein a surface tension of the melt is more dominant than the force ofgravity acting on the melt in the single crystal-growing section. 15.The oxide-series single crystal producing process claimed in claim 13,wherein the melt is being drawn downwardly thereby continuously growingthe oxide-series single crystal body while fresh single crystal rawmaterial is periodically or continuously fed into the crucible.
 16. Theoxide-series single crystal producing process claimed in claim 13,wherein said oxide-series single crystal body has a solid-solutioncomposition.
 17. The oxide-series single crystal producing processclaimed in claim 13, wherein said oxide-series single crystal body has asegregated component.
 18. The oxide-series single crystal producingprocess claimed in claim 13, wherein a laser beam is irradiated upon theoxide-series single crystal body, an output light beam from theoxide-series single crystal body is measured, and a composition ratio ofthe raw material to be fed to the crucible is controlled based on themeasured output light beam.
 19. An oxide-series single crystal-producingApparatus comprising a melting crucible adapted for melting a rawmaterial forming an oxide-series single crystal and having an opening,and a single crystal-growing crucible having a volume smaller than thatof the melting crucible and provided with a drawing hole, wherein theraw material is melted in the melting crucible, and is continuously fedinto the single crystal-growing crucible through said opening, a seedcrystal is contacted with the melt at said drawing hole of the growingcrucible, and the oxide-series single crystal is grown, while the meltis being drawn downwardly through said opening.
 20. The oxide-seriessingle crystal-producing apparatus according to claim 19, which furthercomprises a nozzle portion comprised of a conductive material andextending downwardly from the melting crucible, and an electric powerfeeding mechanism for applying electric power to the nozzle portion tomake the nozzle portion generate heat, said opening being provided at alower end portion of said nozzle portion.
 21. The oxide-series singlecrystal-producing apparatus according to claim 19, which furthercomprises a nozzle portion extending downwardly from the meltingcrucible and having said opening at a lower portion thereof, aheat-generating resistive member arranged to surround said nozzleportion, and an electric power feeding mechanism for applying electricpower to the heat-generating resistive member to make theheat-generating resistive member generate heat.
 22. The oxide-seriessingle crystal-producing apparatus according to claim 19, which furthercomprises a nozzle portion extending downwardly from the meltingcrucible and having said opening at a lower end portion thereof, and aradio frequency induction heating mechanism for heating the nozzleportion through radio frequency induction.
 23. An oxide-series singlecrystal-producing apparatus claimed in claim 19, which further comprisesa raw material feeder for feeding the raw material to the crucible, amoving device for pulling down the oxide-series single crystal body fromthe crucible, a laser beam source for irradiating a laser beam upon theoxide-series single crystal body, a measuring device for measuring anoutput light beam from the oxide-series single crystal body, and acontroller for controlling a composition ratio of the raw material to befed to the crucible based on an output signal from the measuring device.24. An oxide-series single crystal-producing process comprising thesteps of feeding a raw material for an oxide-series single crystal intoa crucible, melting the raw material in the crucible, contacting a seedcrystal with the resulting melt, and growing an oxide-series singlecrystal body from the melt, wherein a laser beam is irradiated upon theoxide-series single crystal body, an output light beam from theoxide-series single crystal body is measured, and a composition ratio ofthe raw material to be fed to the crucible is controlled based on themeasured output light beam.
 25. The oxide-series singlecrystal-producing process according to claim 24, wherein saidoxide-series single crystal body is grown while the melt is being drawndownwardly from the crucible.
 26. The oxide-series singlecrystal-producing process according to claim 24, wherein saidoxide-series single crystal body provides an oxide-series single crystalbody for a laser, said laser beam is irradiated upon said oxide-seriessingle crystal, and a converted light beam, in which a wavelength ofsaid laser beam is converted, is measured.
 27. The oxide-series singlecrystal-producing process according to claim 24, wherein saidoxide-series single crystal has a second harmonic generation effect,said laser beam is irradiated upon the oxide-series single crystal, anda double frequency wave of the laser beam is measured.
 28. Theoxide-series single crystal-producing . process according to claim 24,wherein said laser beam has a wavelength range including a wavelengthcorresponding to a target composition of said oxide-series singlecrystal body, and an output light beam from said oxide-series singlecrystal body is measured by a spectrum analyzer.
 29. The oxide-seriessingle crystal-producing process according to claim 24, wherein a firstlaser beam having a wavelength greater than that corresponding to atarget composition of said oxide-series single crystal body and a secondlaser beam having a wavelength smaller than that corresponding to thetarget composition of said oxide-series single crystal body areirradiated upon the oxide-series single crystal body, and output lightbeams respectively corresponding to said first laser beam and saidsecond laser beam are measured.
 30. The oxide-series singlecrystal-producing process according to claim 24, wherein a crosssectional shape of the oxide-series single crystal body is measured byan optical sensor.